This page shows what was measured, who it was measured in, and what that does not settle.
What Letrozole does in the body
Advanced breast
From the FDA-approved label: The growth of some cancers of the breast is stimulated or maintained by estrogens. , estrogen and/or progesterone receptor positive or receptor unknown) has included a variety of efforts to decrease estrogen levels (ovariectomy, adrenalectomy, hypophysectomy) or inhibit estrogen effects (antiestrogens and progestational agents). These interventions lead to decreased tumor mass or delayed progression of tumor growth in some women.
What happened in people
RNAWiki has not yet published a reviewed conclusion for this use.
§ A fixed RNAWiki sentence
Where this came from
Wording RNAWiki always uses, not a finding about this substance.
No reviewed claim names a result for any goal on this record.
No source is stored against this line.
The limit that matters most
Not recorded.
Where it acts
Not recorded.
Kind of result
No result is published, so no kind of result applies yet
Supervision
Professional supervision is normally required. A regulator classifies this substance in a way that restricts how it is supplied.
What the registries record it as
The substance registry classes this as chemical.
FDA substance registry · 7LKK855W8I · read 2026-08-29
Its recorded molecular formula is C17H11N5, weighing 285.31.
US prescribing information · 1b408ba8-05f7-1cf1-e063-6394a90a42bc · read 2026-08-30
Where each sentence above came from
No recorded sentence describes the change this makes in a way that stands on its own. The page opens with what it is taken for instead, and the recorded explanation follows below.
Shown as the opening line on this page.
No statement of the main limit is recorded.
The four opening statements run to 79 words.
Words this page uses
Four words worth knowing first
Chosen from what this page shows, with each one explained before the word it depends on.
Stand-in result
A stand-in result is a number measured because the real result takes too long.
A picture of it, and where the picture fails
It is like judging a journey by the speedometer rather than by arriving.
Where that stops being true. Speed does predict arrival. Many stand-in results do not predict the real one.
What people get wrong. A stand-in result is often reported as the result itself.
A surrogate endpoint substituted for a clinical endpoint, valid only where the substitution has been shown to hold.
Enzyme
An enzyme is a protein that speeds up one chemical change.
A picture of it, and where the picture fails
An enzyme is like a machine on a production line doing one cut.
Where that stops being true. A machine is switched on and off by a person. Enzymes are controlled by the cell.
What people get wrong. Enzymes are thought to be used up. They are not; they work again and again.
A catalytic protein that lowers the activation energy of a specific reaction.
Receptor
A receptor is a part of a cell that a signal fits into.
A picture of it, and where the picture fails
A receptor is like a lock waiting for one key.
Where that stops being true. A lock either opens or does not. A receptor can be half-triggered, or worn out.
What people get wrong. Fitting a receptor is read as causing a benefit. It causes a step, and nothing more.
A protein that binds a specific ligand and converts that binding into a cellular response.
Pathway
A pathway is a chain of steps inside a cell, each one setting off the next.
A picture of it, and where the picture fails
A pathway is like a row of dominoes.
Where that stops being true. Dominoes fall one way. Pathways loop back and can switch themselves off.
What people get wrong. Changing one step is read as changing the outcome. Other steps often absorb it.
An ordered series of molecular interactions producing a defined cellular change.
What happened in people◇Read from sources, not yet reviewed
What was measured, goal by goal
One row for each goal a registered study measured something for. One column for each kind of thing that could be measured.
Registered studies list 40 outcome measures that RNAWiki could read. A registered study says what someone planned to measure. It does not say what they found. 0 of the matched studies tested this substance, and 0 posted a result.
There is no single score. A strong test result and a weak life result are different facts.
Goals down the side, kinds of measurement across the top. Each cell says what kind of thing was registered, not what was found.
Goal
Life outcome
What a body can do
How a person feels
A test result
A step in the body
Harms
How long
Who was studied
Body weight
∅Nothing in the sources checkedNo registered study lists a life outcome for this goal.
∅Nothing in the sources checkedNo registered study lists a performance measure for this goal.
∅Nothing in the sources checkedNo registered study lists a symptom measure for this goal.
△Only a number moved3 registered test measure.
∅Nothing in the sources checkedNo registered study lists a body-step measure for this goal.
—Not recordedHarms were not a registered measure for this goal.
—Not recordedNo finished study window is recorded.
…Waiting for a reviewerWho was studied is listed further down the page.
Blood sugar
∅Nothing in the sources checkedNo registered study lists a life outcome for this goal.
∅Nothing in the sources checkedNo registered study lists a performance measure for this goal.
∅Nothing in the sources checkedNo registered study lists a symptom measure for this goal.
△Only a number moved1 registered test measure.
∅Nothing in the sources checkedNo registered study lists a body-step measure for this goal.
—Not recordedHarms were not a registered measure for this goal.
—Not recordedNo finished study window is recorded.
…Waiting for a reviewerWho was studied is listed further down the page.
Which registered measures put each goal on this table
Body weight
body weight; body mass index; body composition
Blood sugar
glucose tolerance
Sorted by fixed word lists, version v1. A name the rules do not recognise stays unsorted rather than moving to the nearest column.
What each mark on this table means
∅ Nothing in the sources checked
No registered study lists a life outcome for this goal.
△ Only a number moved
3 registered test measure.
— Not recorded
Harms were not a registered measure for this goal.
… Waiting for a reviewer
Who was studied is listed further down the page.
What happened in people◇Read from sources, not yet reviewed
What happened in people
Each card is one study: the exact question it asked, who was in it, and whether it showed what it set out to show.
5-year Disease-free Survival
✗ The study did not show it
Who was studied
NCT00310180
How many people
10273
Study design
Phase 3
Compared against
Not recorded for this study
Kind of result
Living longer, or avoiding a major event
What was found
Result not recorded on this page
Repeated elsewhere
Unreplicated
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. No limitation is recorded for this study.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
openFDA Drugs@FDA · a recorded source, not a stored snapshot
openFDA NDC Directory · a recorded source, not a stored snapshot
openFDA SPL label · a recorded source, not a stored snapshot
PubChem PUG-REST · a recorded source, not a stored snapshot
Disease free survival.
✗ The study did not show it
Who was studied
NCT00004205
How many people
8028
Study design
Phase 3
Compared against
Not recorded for this study
Kind of result
Living longer, or avoiding a major event
What was found
Result not recorded on this page
Repeated elsewhere
Unreplicated
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. No limitation is recorded for this study.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
openFDA Drugs@FDA · a recorded source, not a stored snapshot
openFDA NDC Directory · a recorded source, not a stored snapshot
openFDA SPL label · a recorded source, not a stored snapshot
PubChem PUG-REST · a recorded source, not a stored snapshot
Invasive Disease-Free Survival (IDFS)
✗ The study did not show it
Who was studied
NCT05514054
How many people
8000
Study design
Phase 3
Compared against
Not recorded for this study
Kind of result
Living longer, or avoiding a major event
What was found
Result not recorded on this page
Repeated elsewhere
Unreplicated
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. No limitation is recorded for this study.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
openFDA Drugs@FDA · a recorded source, not a stored snapshot
openFDA NDC Directory · a recorded source, not a stored snapshot
openFDA SPL label · a recorded source, not a stored snapshot
PubChem PUG-REST · a recorded source, not a stored snapshot
Distant metastasis-free survival at 5 years
✗ The study did not show it
Who was studied
NCT00433589
How many people
6600
Study design
Phase 3
Compared against
Not recorded for this study
Kind of result
Living longer, or avoiding a major event
What was found
Result not recorded on this page
Repeated elsewhere
Unreplicated
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. No limitation is recorded for this study.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
openFDA Drugs@FDA · a recorded source, not a stored snapshot
openFDA NDC Directory · a recorded source, not a stored snapshot
openFDA SPL label · a recorded source, not a stored snapshot
PubChem PUG-REST · a recorded source, not a stored snapshot
Invasive breast cancer-free survival (IBCFS)
✗ The study did not show it
Who was studied
NCT05952557
How many people
5511
Study design
Phase 3
Compared against
Not recorded for this study
Kind of result
Living longer, or avoiding a major event
What was found
Result not recorded on this page
Repeated elsewhere
Unreplicated
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. No limitation is recorded for this study.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
openFDA Drugs@FDA · a recorded source, not a stored snapshot
openFDA NDC Directory · a recorded source, not a stored snapshot
openFDA SPL label · a recorded source, not a stored snapshot
PubChem PUG-REST · a recorded source, not a stored snapshot
The time from the date of randomization to the first occurrence of any of the following events: ipsilateral local or contralateral invasive recurrence, distant recurrence, or death from any cause.
✗ The study did not show it
Who was studied
NCT07349069
How many people
5500
Study design
Phase 3
Compared against
Not recorded for this study
Kind of result
Living longer, or avoiding a major event
What was found
Result not recorded on this page
Repeated elsewhere
Unreplicated
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. No limitation is recorded for this study.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
openFDA Drugs@FDA · a recorded source, not a stored snapshot
openFDA NDC Directory · a recorded source, not a stored snapshot
openFDA SPL label · a recorded source, not a stored snapshot
PubChem PUG-REST · a recorded source, not a stored snapshot
What we know
RNAWiki holds 6 written-up human studies for this substance, each with the question it asked.
How we know it
Each card names the study, the number of people and what the study set out to measure.
What this does not prove
These summaries were written by a person and have not been signed off as reviewed claims.
Why it matters
A study that failed is as informative as one that worked, and both are here.
What we still do not know
No reviewed claim exists, so no exact population, effect size or interval is published yet.
What happened in people◇Read from sources, not yet reviewed
How close this is to real life
The top step is something a person would feel or care about. The bottom is a guess from software. Filled steps are where evidence exists for this substance.
■Living longer, or avoiding a major eventEvidence recorded. Death, a heart attack, a stroke, a hospital stay.8 registered measures of this kind. 6 written-up studies measured this and did not show a benefit.
■What a body can do day to dayEvidence recorded. Walking, dressing, breathing, recovering.1 registered measure of this kind.
■Measured performanceEvidence recorded. How much was lifted, how far was run, how fast.1 registered measure of this kind.
□Symptoms and quality of lifeNo evidence recorded. Pain, tiredness, mood, sleep, as the person rated it.No registered study measures this.
■A number that stands in for healthEvidence recorded. Cholesterol, blood sugar, bone density. A stand-in, not the thing itself.9 registered measures of this kind.
■A step measured inside a personEvidence recorded. Something measured in human tissue or human cells.A human record sits on the stored organism ladder.
■AnimalsEvidence recorded. Mice, rats, dogs. Useful for ideas, not proof about people.Stored records in Mouse, Rat, Non-human primate. A result in animals says what to test next. It does not say what happens in people.
■Cells in a dishEvidence recorded. Cells or chemistry on a bench, far from a whole body.Stored mechanism abstracts describe steps measured in cells or tissue.
□A guess from softwareNo evidence recorded. Nobody measured it. RNAWiki never publishes one as a finding.RNAWiki stores no prediction for this record. Software can suggest a link. RNAWiki does not publish one as a finding.
Higher on these steps means closer to something a person would feel. It does not mean better done.
What it would be like to take◇Read from sources, not yet reviewed
Felt, measured, or meaningful
Three different things that get called the same word. Registered studies measured all three, and mixing them is how a blood test becomes a health claim.
Felt
Things a person could notice without a test.
No registered study measured anything of this kind.
Measured
Things only a test, a scale or a device shows.
lumbar spine bone mineral density
body weight
body mass index
waist circumference
body composition
exercise capacity
glucose tolerance
bone mineral density of the lumbar spine
bone mineral density from baseline to month 36
bone mineral density
Meaningful
Things that change how a life goes, not only a number.
disease free survival
partial remission
progression free survival
5 year disease free survival
overall survival of
overall survival
disease free survival in premenopausal
distant metastasis free survival at 5 years
A registered study says what someone planned to measure. It does not say what they found. A number moving is not the same as a life going better. The two are shown apart here.
Felt, but not shown to help. A person notices a change. No study showed it leads anywhere good.
Measured, but not felt. A number moves. The person notices nothing. Both can be true.
Measured, but not shown to matter. A number moves in the good direction. Nobody showed that lives went better.
Matters, but takes years. The result that counts may take longer than anyone would keep watching.
Names that fit none of the three (22)
adult height relative to general population
objective tumour response
time to tumor progression
objective response
time to progression
clinical response rate
6 month tumor volume compared to baseline using mammography
safety
feasibility
t from baseline to month 36
z from baseline to month 36
objective response rate
objective tumor response
pregnancy rate
overall response rate as measured by recist
pathological complete response
dose limiting toxicity
pathologic complete response
ovulation rate by ultrasonography
clinical benefit response rate
These are harms, study-process measures, or names the rules did not recognise. They are shown rather than dropped.
What it would be like to take◇Read from sources, not yet reviewed
How long anything takes
Nine different lengths of time that get confused with each other. None of them is worked out from another.
Before anything is noticed.RNAWiki does not store this separately, and never works it out from another figure on this page.
Before a test result moves.RNAWiki does not store this separately, and never works it out from another figure on this page.
Before performance moves.RNAWiki does not store this separately, and never works it out from another figure on this page.
How long the result was watched.No finished study window is recorded for a study that tested this substance.
How long people took it.How long people actually took it is not stored. The study window is not the same thing.
How long people were followed.Follow-up length is not stored separately. It is never read off the study window, which would be a different thing.
How fast the body clears it. 2 days
Read from the label, which states: “Letrozole’s terminal elimination half-life is about 2 days and steady-state plasma concentration after daily 2.5 mg dosing is reached in 2 to 6 weeks.”
How long effects linger.RNAWiki does not store this separately, and never works it out from another figure on this page.
Beyond the studies. Nothing is recorded about the long term.
The longest finished study sets the edge of what anyone measured.
A study window is not how long people took it, and neither is how long they were followed. Where RNAWiki holds only one of the three, it shows one.
What is missing or unclear◇Read from sources, not yet reviewed
Were people like you studied?
RNAWiki cannot tell whether a study fits you. It can show who was in it, and where the result stops carrying.
Who was studied
People similar to this profile were included.
Letrozole tablet is an aromatase inhibitor indicated for: Adjuvant treatment of postmenopausal women with hormone receptor positive early breast cancer ( 1.1 ) Extended adjuvant treatment of postmenopausal women with early breast cancer who have received prior standard adjuvant tamoxifen therapy ( 1.2 ) First and second-line treatment of postmenopausal women with hormone receptor positive or unknown advanced breast…
Who is missing from the studies
Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
What the label states about particular groups
On pediatric, the label states: “The safety and effectiveness in pediatric patients have not been established.”
US prescribing information · 1b408ba8-05f7-1cf1-e063-6394a90a42bc · read 2026-08-30
On older people, the label states: “For the extended adjuvant setting (MA-17), more than 5,100 postmenopausal women were enrolled in the clinical study.”
US prescribing information · 1b408ba8-05f7-1cf1-e063-6394a90a42bc · read 2026-08-30
On people who are pregnant, the label states: “Risk Summary Based on postmarketing reports, findings from animal studies and the mechanism of action, letrozole can cause fetal harm and is contraindicated for use in pregnant women.”
US prescribing information · 1b408ba8-05f7-1cf1-e063-6394a90a42bc · read 2026-08-30
On people who are breastfeeding, the label states: “Risk Summary It is not known if letrozole is present in human milk.”
US prescribing information · 1b408ba8-05f7-1cf1-e063-6394a90a42bc · read 2026-08-30
Where the result stopped carrying
This is a scope explorer, not a diagnosis engine.
It shows who was studied so you can see whether people similar to you were included.
RNAWiki cannot tell whether a study fits you. It can show who was in it.
What it would be like to take◇Read from sources, not yet reviewed
Why it might seem to do nothing
A real effect and a noticed effect are different things. These are the recorded reasons the two come apart.
It was studied for a different goal
The studies measured something else entirely.
On this record: Some registered studies measured things that match no goal on this page.
It was studied in different people
The people in the studies were not much like the reader.
On this record: Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
The evidence may simply be wrong
Small early studies often do not hold up.
On this record: RNAWiki has not yet published a reviewed conclusion for this use.
Other reasons RNAWiki checked and found nothing for (10)
A different form was studied
The studied form is not the form on the shelf. Nothing in this record points to this reason.
There was nothing to correct
Where a level is already normal, topping it up may change nothing. Nothing in this record points to this reason.
Something else had to happen too
In the studies it was paired with training, a diet or another treatment. Nothing in this record points to this reason.
The change is too small to feel
A real change can still sit below what a person notices. Nothing in this record points to this reason.
Day-to-day swing hides it
Sleep, food, stress and time of day move most numbers more than this would. Nothing in this record points to this reason.
Not enough time yet
The studies ran longer than the person has waited. Nothing in this record points to this reason.
It was not taken as studied
Missed days change the result, and studies count them. Nothing in this record points to this reason.
Something else changed at the same time
Two changes at once cannot be told apart afterwards. Nothing in this record points to this reason.
The product may not be what it says
Contents of a sold product are not always what the label states. Nothing in this record points to this reason.
No recorded reason
RNAWiki has nothing stored that would explain it. Nothing in this record points to this reason.
None of these is a reason to take more. Taking more is not a step this page ever suggests.
What it would be like to take◇Read from sources, not yet reviewed
What taking it involves
The recorded facts about getting hold of it and using it. Nothing here is a suggestion about what you should do.
How it is supplied
Prescription only
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
Read from the recorded approval status.
No source is stored against this line.
Form and route
Oral
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form and route recorded on this substance.
No source is stored against this line.
Who oversees it
Professional supervision is normally required. A regulator classifies this substance in a way that restricts how it is supplied.
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
Suppression classes recorded: S3.
No source is stored against this line.
What is in the pack
Sold as tablet, tablet, film coated, given by the oral route.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on how this is sold and what that means for what is in the pack.
No source is stored against this line.
Where it is registered
Regulatory records are listed in the technical disclosure at the foot of this page.
# Counted from records
Where this came from
A count of rows RNAWiki holds. It describes our records, not your body.
Register entries are stored per jurisdiction and shown with their dates.
No source is stored against this line.
Why people stop
Not recorded.
∅ Nothing recorded
Where this came from
RNAWiki holds nothing here and says so rather than guessing.
No record of why people stopped taking it is stored for this substance.
No source is stored against this line.
What it would be like to take∅Nothing found in the sources checked
What can go wrong
Sorted by where each line came from. A regulator's label and a report somebody sent in are not the same kind of fact.
∅Nothing found in the sources checked
No harm is recorded against this substance in the sources RNAWiki checked. Finding nothing is not the same as showing there is nothing.
The sources listed were searched and held nothing. That is not the same as nothing existing.
Reports sent to a regulator
These are reports people sent to a regulator. They do not show the medicine caused the reaction.
Nobody counted how many people took the medicine and reported nothing.
The same event can be reported more than once, and many reports are incomplete.
News coverage, lawsuits and new warnings change how often people report.
A count is not a rate and not a risk.
Letrozole appears in spontaneous reports to regulators. Across the 10 most-reported reaction terms, 10687 reaction mentions were counted. One report can name several reactions.
open-targets-adr · recorded 2026-06-24 · a recorded source, not a stored snapshot
Over a long time. No completed tested study window is recorded, so long-term effects are not established by the registry record.
Groups the studies covered thinly. Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
What is missing or unclear◇Read from sources, not yet reviewed
Does the exact form matter?
Evidence belongs to the exact thing that was tested. A different salt, a different mixture or a different preparation is a different question.
The form that was studied
Oral
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form used in the studies cited on this page.
No source is stored against this line.
What is sold
Not recorded.
∅ Nothing recorded
Where this came from
RNAWiki holds nothing here and says so rather than guessing.
Nothing further is recorded about which forms are sold.
No source is stored against this line.
What is recorded as being sold
36 products list this as an active ingredient in the United States drug directory. 36 of them contain it and nothing else.
FDA National Drug Code directory · 23155-875 · read 2026-08-29
They are sold as powder, tablet and tablet, film coated, taken oral.
FDA National Drug Code directory · 23155-875 · read 2026-08-29
The regulator's established pharmacologic class for it is aromatase inhibitor [epc] and aromatase inhibitors [moa].
FDA National Drug Code directory · 23155-875 · read 2026-08-29
24 published labels name it as an active ingredient. 24 of them describe this substance alone, which is where its own label text on this page comes from.
US prescribing information · 1b408ba8-05f7-1cf1-e063-6394a90a42bc · read 2026-08-29
Those labels are classed as human prescription drug.
US prescribing information · 1b408ba8-05f7-1cf1-e063-6394a90a42bc · read 2026-08-29
Letrozole is oral at 3 DOSAGE FORMS AND STRENGTHS 2.5 mg tablets: yellow round, biconvex, film coated tablets imprinted with 'LT' on one side and plain on other side. 2.5 mg tablets ( 3 ), recorded as fda label in effect 2024-06-19 in the United States.
US prescribing information · 1b408ba8-05f7-1cf1-e063-6394a90a42bc · read 2026-08-30
Recorded price in US: 0.15111 USD per one unit as the pricing file counts it — a tablet, capsule, patch or single item, across 14 priced products whose strengths and pack forms differ, as of 2026-08-26, paid by retail pharmacies buying the product, as surveyed by the Centers for Medicare & Medicaid Services. It is not a list price, an insurance price, or what anyone pays at a counter..
Recorded source · 2026-08-26 · read 2026-08-28
Evidence carries across two names for one substance. It does not carry across a salt, a mirror form or a mixture.
What it would be like to take◇Read from sources, not yet reviewed
What you could measure
This one is decided with a clinician, so this section holds questions to ask rather than a plan to run.
Self-experiment planning is not offered for a prescription or clinician-supervised medicine. The questions below are for a clinician or pharmacist.
Questions worth asking
Which of the trials of Letrozole studied people like me?
What was measured, and for how long?
Was the result a laboratory value or a health outcome?
What would we watch for, and when would we stop?
Tracking can show whether something changed for you. It cannot show what caused it.
RNAWiki records evidence. It does not say whether this substance is right for you.
What is missing or unclear◇Read from sources, not yet reviewed
What nobody knows yet
Open questions, each with why it is open and what would close it.
Missing populations
Which groups were under-represented in the studies has not been recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing long-term data
No completed tested study window is recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
No reviewed conclusion
RNAWiki has not yet published a reviewed conclusion for this use.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing interaction studies
No interaction was found in the registers checked. Not finding one is not the same as showing there is none.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Formulation uncertainty
Several salts, forms or products of Letrozole are recorded. Results from one form may not transfer to another.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Mechanism not reviewed
No reviewed mechanism story exists for this substance.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
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7LKK855W8I
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200064
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24 approved applications cover products containing this substance. The earliest was NDA020726, approved 19970725 to NOVARTIS PHARMS.
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5 questions this page could not answer
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Recorded evidence blocks (14)
Q2
What did Letrozole's largest trial (10273 people) and its longest (29 years) measure?
10273 people in Letrozole's largest registered study, 29 years in its longest registered window, measuring Changes in Senescence and Secondary Biomarkers, Including TMEM, Mena, and 67LR. ClinicalTrials.gov · 2026-09-01
255 phase2, 139 phase3, 77 phase1, 60 na, 51 phase4, 22 na or unstated, 14 early phase1; NCT00001521; 2024-04-01. Last human test completed 2026, NCT05150652.
Interpretation These counts include studies where Letrozole was a comparison treatment, a background treatment or an exposure in an observational study, and the longest window may be a planned end date. Trial roles have not yet been classified for this record.
Show the evidence
phase2
255
phase3
139
phase1
77
na
60
phase4
51
na or unstated
22
2 more recorded rows
early phase1
14
Last recorded human testNCT05150652
2026-06-10
recorded 2026-09-01 · last checked 2026-09-04
Q3
From mouse to human: where has Letrozole shown biomarker?
Letrozole's half-life is 2 days — which schedules were studied?
2 days, the half-life Letrozole's label states. openfda-label · 3cc750a5-cc88-4b42-b4ab-a87e760f291d · 2026-08-30
Show the evidence
half life
2 days; Letrozole’s terminal elimination half-life is about 2 days and steady-state plasma concentration after daily 2.5 mg dosing is reached in 2 to 6 weeks.
metabolism
Elimination Metabolism and Excretion: Metabolism to a pharmacologically-inactive carbinol metabolite (4,4'-methanol-bisbenzonitrile) and renal excretion of the glucuronide conjugate of this metabolite is the major pathway of letrozole clearance.
recorded 2026-08-30 · last checked 2026-09-04
Q7
Which of 5 year disease free survival, 6 month tumor volume compared to baseline using mammography and adult height relative to general population did Letrozole's trials measure?
5 year disease free survival, 6 month tumor volume compared to baseline using mammography and adult height relative to general population lead 40 outcome terms across Letrozole's trials. ClinicalTrials.gov · 2026-09-01
Interpretation time to tumor progression, lumbar spine bone mineral density, objective response, time to progression, partial remission and body weight follow.
Show the evidence
adult height relative to general population
1
disease free survival
1
objective tumour response
1
time to tumor progression
1
lumbar spine bone mineral density
1
objective response
1
14 more recorded rows
time to progression
1
partial remission
1
body weight
1
body mass index
1
waist circumference
1
body composition
1
exercise capacity
1
glucose tolerance
1
bone mineral density of the lumbar spine
1
progression free survival
1
clinical response rate
1
6 month tumor volume compared to baseline using mammography
1
safety
1
feasibility
1
recorded 2026-09-01 · last checked 2026-09-04
Q8
Which of Letrozole's 142 ongoing trials reports first?
"Hormone Therapy With or Without Combination Chemotherapy in Treating Women Who Have Undergone Surgery for Node-Negative Breast Cancer (The TAILORx Trial)"; n 10273; "5-year Disease-free Survival"; 2030-09-30
NCT00999804
"Extension Study of Lapatinib Plus Herceptin With or Without Endocrine Therapy"; n 128; "Pathologic Complete Response"; 2026-01
NCT01068249
"Letrozole and RAD001 With Advanced or Recurrent Endometrial Cancer"; n 42; "Number of Participants With Objective Response Rate"; 2028-04-30
NCT01272037
"Tamoxifen Citrate, Letrozole, Anastrozole, or Exemestane With or Without Chemotherapy in Treating Patients With Invasive RxPONDER Breast Cancer"; n 5018; "Invasive Disease-Free Survival (IDFS)"; 2027-01-08
NCT01674140
"S1207 Hormone Therapy With or Without Everolimus in Treating Patients With Breast Cancer"; n 1939; "Invasive Disease-Free Survival (IDFS)"; 2030-01
NCT01872260
"Study of LEE011, BYL719 and Letrozole in Advanced ER+ Breast Cancer"; n 255; "Incidence of Dose limiting toxicities (DLTs) - Phase lb only"; 2027-02-26
14 further recorded trials
NCT02057133
"A Study of LY2835219 (Abemaciclib) in Combination With Therapies for Breast Cancer That Has Spread"; n 198; "Number of Participants with One or More Drug-Related Adverse Events"; 2026-12
NCT02221999
"Weekly Paclitaxel and Cisplatin to Treat Hormone Receptor Positive and Triple Negative Breast Cancer Patients"; n 250; "pathological complete remission rate"; 2029-01
NCT02246621
"A Study of Nonsteroidal Aromatase Inhibitors Plus Abemaciclib (LY2835219) in Postmenopausal Women With Breast Cancer"; n 493; "Progression Free Survival (PFS)"; 2026-12
NCT02338310
"Trial of Perioperative Endocrine Therapy - Individualising Care"; n 4486; "Time to recurrence"; 2034-04
NCT02603679
"Neoadjuvant Response-guided Treatment of Luminal B-type Tumors and Luminal A-type Tumors With Node Metastases"; n 181; "Radiological Objective Response Rate after Completion of the First 12-week Period of Primary Medical Treatment"; 2031-12-31
NCT02712723
"Letrozole Plus Ribociclib or Placebo as Neo-adjuvant Therapy in ER-positive, HER2-negative Early Breast Cancer"; n 121; "Rate of PEPI Score 0 at Surgery Between Ribociclib Containing Arms (Combined) vs. Letrozole Alone Arm."; 2026-12
NCT02763566
"A Study of Abemaciclib (LY2835219) in Participants With Breast Cancer"; n 463; "Progression Free Survival (PFS) (Abemaciclib + NSAI & Placebo NSAI)"; 2028-03
NCT02764541
"Palbociclib and Endocrine Therapy for LObular Breast Cancer Preoperative Study (PELOPS)"; n 195; "Difference in Anti-proliferative Activity of Patients Given Letrozole Versus Tamoxifen During the Window Phase"; 2031-04
NCT02778685
"Pembrolizumab, Endocrine Therapy, and Palbociclib in Treating Postmenopausal Patients With Newly Diagnosed Metastatic Stage IV Estrogen Receptor Positive Breast Cancer"; n 47; "Response Rate (Complete Response or Partial Response)"; 2026-03-30
NCT02947685
"Randomized, Open Label, Clinical Study of the Targeted Therapy, Palbociclib, to Treat Metastatic Breast Cancer"; n 518; "Progression-free Survival (PFS) as Assessed by Investigator"; 2026-07-31
NCT03006172
"To Evaluate the Safety, Tolerability, and Pharmacokinetics of Inavolisib Single Agent in Participants With Solid Tumors and in Combination With Endocrine and Targeted Therapies in Participants With Breast Cancer"; n 200; "Stage 1: Percentage of Participants With Dose Limiting Toxicities"; 2026-12-31
NCT03008408
"A Phase II, Two-Arm Study of Everolimus and Letrozole, +/- Ribociclib (Lee011) in Patients With Advanced or Recurrent Endometrial Carcinoma"; n 90; "Clinical benefit rate (CBR)"; 2028-08-31
NCT03011684
"Fertility Preservation Using Tamoxifen and Letrozole in Estrogen Sensitive Tumors Trial"; n 309; "Mature Oocyte Yield"; 2028-03-31
NCT03122197
"Study of Letrozole in Recurrent Gliomas"; n 39; "Overall Letrozole AUC in tumor tissue."; 2027-12
recorded 2026-09-01 · last checked 2026-09-04
Q9
Which running trial of Letrozole could settle lifespan?
NCT02947685 measures Progression-free Survival (PFS) as Assessed by Investigator, reading out 2026-07-31.
40 open trials; n 518; "Randomized, Open Label, Clinical Study of the Targeted Therapy, Palbociclib, to Treat Metastatic Breast Cancer"
Show the evidence
Trial
NCT02947685
"Randomized, Open Label, Clinical Study of the Targeted Therapy, Palbociclib, to Treat Metastatic Breast Cancer"; n 518; "Progression-free Survival (PFS) as Assessed by Investigator"; 2026-07-31
NCT05890287
"A Study of Chidamide Plus Endocrine in Maintenance Treatment of HR+/HER2- Breast Cancer After First-line Chemotherapy"; n 60; "Progression-free survival"; 2026-10-01
NCT02246621
"A Study of Nonsteroidal Aromatase Inhibitors Plus Abemaciclib (LY2835219) in Postmenopausal Women With Breast Cancer"; n 493; "Progression Free Survival (PFS)"; 2026-12
NCT04393285
"Abemaciclib and Letrozole to Treat Endometrial Cancer"; n 53; "Progression-free survival"; 2026-12-31
NCT01272037
"Tamoxifen Citrate, Letrozole, Anastrozole, or Exemestane With or Without Chemotherapy in Treating Patients With Invasive RxPONDER Breast Cancer"; n 5018; "Invasive Disease-Free Survival (IDFS)"; 2027-01-08
NCT04546009
"A Study Evaluating the Efficacy and Safety of Giredestrant Combined With Palbociclib Compared With Letrozole Combined With Palbociclib in Participants With Estrogen Receptor-Positive, HER2-Negative Locally Advanced or Metastatic Breast Cancer (persevERA Breast Cancer)"; n 992; "Progression-Free Survival (PFS), as Determined by the Investigator According to RECIST v1.1"; 2027-07-31
14 further recorded trials
NCT06979596
"A Study of MK-5684 in People With Certain Solid Tumors (MK-5684-015/OMAHA-015)"; n 250; "Progression-Free Survival (PFS) - All Cohorts"; 2027-11-04
NCT07024173
"A Phase 3 Study of HRS-8080 Versus Treatment Chosen by Physicians in Locally Advanced and Metastatic Breast Cancer"; n 240; "Progression free survival (PFS) evaluated by the blinded independent central review (BICR)."; 2027-12
NCT04095364
"Letrozole With or Without Paclitaxel and Carboplatin in Treating Patients With Stage II-IV Ovarian, Fallopian Tube, or Primary Peritoneal Cancer"; n 450; "Progression-free survival (PFS)"; 2028-02-01
NCT02763566
"A Study of Abemaciclib (LY2835219) in Participants With Breast Cancer"; n 463; "Progression Free Survival (PFS) (Abemaciclib + NSAI & Placebo NSAI)"; 2028-03
NCT04964934
"Phase III Study to Assess AZD9833+ CDK4/6 Inhibitor in HR+/HER2-MBC With Detectable ESR1m Before Progression (SERENA-6)"; n 315; "Progression-free survival (PFS) assessed by the Investigator as defined by response evaluation criteria in solid tumors (RECIST version 1.1)"; 2028-09-01
NCT07285382
"Different Doses of Dalpicicl Combined With Letrozole in the First-line Treatment of HR-positive, HER2-negative Advanced Breast Cancer"; n 120; "Progression - Free Survival (PFS)"; 2028-12-31
"Letrozole in Uterine Leiomyosarcoma"; n 40; "Progression Free Survival"; 2029-07-30
NCT05826964
"Levels of Circulating Tumor DNA as a Predictive Marker for Early Switch in Treatment for Patients With Metastatic (Stage IV) Breast Cancer"; n 24; "Progression-Free Survival 1 (PFS1) Among Participants in Step 2"; 2029-07-31
NCT07391774
"Testing Whether Hormone Therapy With Ribociclib is as Effective as Chemotherapy Followed by Hormone Therapy With Ribociclib for the Treatment of High Anatomic Stage Breast Cancer With Low Recurrence Risk, The RxFINE-Low Trial"; n 1978; "Invasive breast cancer-free survival (iBCFS)"; 2029-07-31
NCT05467891
"Ribociclib And Endocrine Treatment of Physician's Choice for Locoregional Recurrent, Resected Hormone Receptor Positive HER2 Negative Breast Cancer"; n 200; "Recurrence Free Survival (RFS)"; 2029-08-15
NCT05601700
"Letrozole for Estrogen/Progesterone Receptor Positive Low-grade Serous Epithelial Ovarian Cancer (LEPRE Trial)"; n 132; "Progression-free survival (PFS)"; 2029-09-22
NCT01674140
"S1207 Hormone Therapy With or Without Everolimus in Treating Patients With Breast Cancer"; n 1939; "Invasive Disease-Free Survival (IDFS)"; 2030-01
NCT04569747
"A Single Arm Phase II Study of ADjuvant Endocrine Therapy, Pertuzumab, and Trastuzumab for Patients With Anatomic Stage I Hormone Receptor-positive, HER2-positive Breast Cancer"; n 393; "Invasive Disease Free Survival at 3 Years"; 2030-09-01
Q10
Which 134 trials of Letrozole posted no result?
Posted no result
134 of 134 completed trials
Registrations
NCT00014638, NCT00003140, NCT00134680, NCT00291109, NCT00044291 and NCT00648063, and 128 more
Completion dates
oldest 2002-03; newest 2024-09-02
Show the evidence
Trial
NCT00014638
2002-03
NCT00003140
2003-10
NCT00134680
2005-07
NCT00291109
2005-07
NCT00044291
2006-01
NCT00648063
2006-01
14 further recorded trials
NCT00648154
2006-01
NCT00240942
2006-06
NCT00610077
2006-07
NCT00237211
2006-10
NCT00161291
2006-11
NCT00107016
2007-04
NCT00114270
2007-06
NCT01367626
2008-04
NCT01367652
2008-04
NCT01375452
2008-05
NCT01372982
2008-06
NCT00911313
2009-01
NCT00237133
2009-01-21
NCT00238316
2009-02-10
Q11
At the median, Letrozole's trials enrolled 97 people — anything larger?
Median enrolment
97
Largest enrolment
10273
Registered trials counted
564
Q12
What do 10687 spontaneous reports say about Letrozole — and not say?
These are reports people sent to a regulator. They do not show the medicine caused the reaction. Nobody counted how many people took the medicine and reported nothing. The same event can be reported more than once, and many reports are incomplete. News coverage, lawsuits and new warnings change how often people report. A count is not a rate and not a risk.
Letrozole appears in spontaneous reports to regulators. Across the 10 most-reported reaction terms, 10687 reaction mentions were counted: malignant neoplasm progression 1697; fatigue 1457; arthralgia 1414; neutropenia 1390. open-targets-adr · CHEMBL1444 · 2026-06-24
Show the evidence
malignant neoplasm progression
1697
fatigue
1457
arthralgia
1414
neutropenia
1390
metastases to bone
950
disease progression
792
4 more recorded rows
neoplasm progression
783
metastases to liver
751
breast cancer
747
breast cancer metastatic
706
recorded 2026-06-24 · last checked 2026-09-04
Q13
Letrozole and CYP2A6, CYP2C19 and CYP3A4: shared by which compounds?
CYP2A6, CYP2C19 and CYP3A4 appear in Letrozole's recorded interaction sentences, 4 in all. openfda-label+europepmc · 2026-08-30
Interpretation pharmacokinetics
Show the evidence
CYP2A6
pharmacokinetics
In human microsomes with specific CYP isozyme activity, CYP3A4 metabolized letrozole to the carbinol metabolite while CYP2A6 formed both this metabolite and its ketone analog.
pharmacokinetics
In human liver microsomes, letrozole inhibited CYP2A6 and CYP2C19, however, the clinical significance of these findings is unknown.
CYP2C19pharmacokinetics
In human liver microsomes, letrozole inhibited CYP2A6 and CYP2C19, however, the clinical significance of these findings is unknown.
CYP3A4pharmacokinetics
In human microsomes with specific CYP isozyme activity, CYP3A4 metabolized letrozole to the carbinol metabolite while CYP2A6 formed both this metabolite and its ketone analog.
recorded 2026-08-30 · last checked 2026-09-04
Q14
Was Letrozole studied with fasting?
fasting is named in Letrozole's label sentences: "The studies suggested that <i>S. miltiorrhiza</i> extract combined with letrozole (LET) was more effective in improving pregnancy rate (RR: 2.60, 95% CI: 1.06 to 6.39, <i>P</i>=0.04) compared to LET alone. <i>S. miltiorrhiza</i> extract was associated with decreased fasting blood glucose (MD:…" openfda-label+europepmc · 2026-08-30
1 recorded statement; fasting
Show the evidence
fasting
The studies suggested that <i>S. miltiorrhiza</i> extract combined with letrozole (LET) was more effective in improving pregnancy rate (RR: 2.60, 95% CI: 1.06 to 6.39, <i>P</i>=0.04) compared to LET alone. <i>S. miltiorrhiza</i> extract was associated with decreased fasting blood glucose (MD: -0.25, 95% CI: -0.37 to -0.13, <i>P</i> < 0.0001), fasting insulin (MD: -1.16, 95% CI: -1.74 to -0.58,…
recorded 2026-08-30 · last checked 2026-09-04
Q15
What is recorded about Letrozole and mTOR?
"JFP improved endocrine and ovarian dysfunction in letrozole-induced PCOS rats, with its effects associated with modulation of CYP17A1/CYP19A1-mediated steroidogenesis, PI3K/Akt/mTOR-related signaling, and inflammatory-apoptotic pathways." — where Letrozole and mTOR appear together. Europe PMC · pathway abstract search · 2026-08-13
"JFP improved endocrine and ovarian dysfunction in letrozole-induced PCOS rats, with its effects associated with modulation of CYP17A1/CYP19A1-mediated steroidogenesis, PI3K/Akt/mTOR-related signaling, and inflammatory-apoptotic pathways."
PMID 42155917
"This review focuses on the biological mechanisms that may provide an avenue for improved clinical outcomes by enhancing oocyte quality through more targeted therapy: differing follicle-stimulating hormone isoforms; follicle-stimulating hormone dose effects; distinct signaling pathways of luteinizing hormone and human chorionic gonadotropin (hCG); androgen priming; growth hormone; letrozole…"
PMID 41339350
"Based on preclinical studies showing synergism with simultaneous inhibition of the estrogen receptor (ER), CDK4/6 and PI3K pathways and based on window of opportunity studies showing that metformin suppresses PI3K/mTOR signaling in endometrial cancer (EC), we conduct a non-randomized phase 2 study of letrozole/abemaciclib/metformin in ER positive endometrioid EC (NCT03675893)."
sirtuinPMID 35538794
"The IC50 concentration of SIRT1 activator (SRT1720), SIRT1 inhibitor (EX527), and aromatase inhibitors (letrozole and fadrozole) was determined by the XTT method."
recorded 2026-08-13 · last checked 2026-09-04
Where it is registeredIdentifiers, relations and other names
ChEMBL ATC CC BY-SA · ClinicalTrials.gov — US Government work · Europe PMC — metadata only, under the recorded legal gate · Open Targets 26.06 — CC0 · derived from this page's own recorded fields; no external licence · mixed register set; per-register licences in docs/specs/corpus-20k-sources.md · openFDA / DailyMed — US Government work
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✓ public claims reviewed: 0 reviewed claim(s); drafts are never rendered
✓ source coverage passed: 11 source rows
✓ no critical contamination: no quarantine open
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This is a record of evidence. It is not medical advice, and it does not say this substance suits you. Nothing here says any substance on RNAWiki is appropriate for a child.