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Drug

Letrozole

In clinical development
ClassCytochrome P450 19A1 inhibitorEmerging researchLate-stage developmentRising momentum

Also known as Femara, Letrozol.

RxNorm72965ChEMBLCHEMBL1444ATCL02BG04UNII7LKK855W8I
10
Research papers
47
Active clinical trials
Aromatase
Primary target
Latest activity
beta

Recent clinical, regulatory, research and industry developments relating to this drug.

Clinical Outcomes of Letrozole-induced Endometrial Preparation Regimens Versus Conventional Endometrial Preparation Regimens Including Natural Cycle, Hormone Replacement Regimens in FET, a Randomized Controlled Study

Clinical trial2026-08-01Primary completion · ClinicalTrials.gov

A Phase 2, Randomized, Open-Label Dose Optimization and Phase 3, Randomized, Double-Blind, Placebo-Controlled Study of LY4064809 Combined With a CDK4/6 Inhibitor and Endocrine Therapy in Adults With HR+, HER2-Advanced Breast Cancer With a PIK3CA Mutation Who Received No Prior Treatment for Advanced Breast Cancer (PIKALO-2)

Clinical trial2026-07-30Results expected Q2 2029 · ClinicalTrials.gov

Letrozole for Treatment of Uterine Fibroids: A Randomized, Placebo-Controlled Trial

Clinical trial2026-07-22Results expected Q3 2028 · ClinicalTrials.gov

A Phase II, Open-Label, Multicenter Study Evaluating the Safety and Efficacy of Neoadjuvant Treatment With Inavolisib Combinations in Patients With Untreated, Early-stage, PIK3CA-Mutated Breast Cancer

Clinical trial2026-07-16Results expected Q3 2027 · ClinicalTrials.gov

An Exploratory Study to Evaluate the Efficacy and Safety of Kumorixilib Combined With Capecitabine and Letrozole as Neoadjuvant Therapy for HR-Positive, HER2-Negative Breast Cancer

Clinical trial2026-07-08Results expected Q1 2028 · ClinicalTrials.gov

Elacestrant Versus Standard Endocrine Therapy in Women and Men With Node-positive, Estrogen Receptor-positive, HER2-negative, Early Breast Cancer With High Risk of Recurrence-A Global, Multicenter, Randomized, Open-label Phase 3 Study

Clinical trial2026-07-08Results expected Q3 2029 · ClinicalTrials.gov

An Open-label, Multi-center, Phase I/II Study of GVV858 as a Single Agent and in Combination With Endocrine Therapy in Patients With Advanced Hormone Receptor Positive, HER2- Negative Breast Cancer and Other Advanced Solid Tumors

Clinical trial2026-07-07Results expected Q2 2031 · ClinicalTrials.gov

Clinical Study of Local and Systemic Biological Impact of GLP1/GIP-Receptor Agonists in Patients With Breast Cancer: The CLARA Trial

Clinical trial2026-07-07Results expected Q1 2028 · ClinicalTrials.gov

Chronic Aromatase Inhibition Attenuates Synaptic Plasticity in Ovariectomized Mice.

Research2024-11-26eNeuro

Abemaciclib plus a nonsteroidal aromatase inhibitor as initial therapy for HR+, HER2- advanced breast cancer: final overall survival results of MONARCH 3.

Research2024-05-08Annals of oncology : official journal of the European Society for Medical Oncology

Efficacy, safety, and biomarker analysis of nivolumab in combination with abemaciclib plus endocrine therapy in patients with HR-positive HER2-negative metastatic breast cancer: a phase II study (WJOG11418B NEWFLAME trial).

Research2023-09-01Journal for immunotherapy of cancer

Clinical considerations of the role of palbociclib in the management of advanced breast cancer patients with and without visceral metastases.

Research2018-03-01Annals of oncology : official journal of the European Society for Medical Oncology

Profile

Identifiers & mechanism

Canonical identifiers, marketed brand names and mechanism, resolved across RxNorm, ChEMBL and ATC.

Canonical name
Letrozole
Aliases & brands
FemaraLetrozol
RxNorm CUI
72965
ChEMBL ID
CHEMBL1444
ATC codes
L02BG04
UNII
7LKK855W8I
Primary mechanism
Cytochrome P450 19A1 inhibitor

Pharmacology & targets

1 target

Known molecular targets and mechanisms supported by curated pharmacology databases.

Aromatase
CYP19A1 · P11511
INHIBITORCytochrome P450 19A1 inhibitor

Clinical trials

190 trials

The current development programme across all trial phases — status mix, phase distribution and the late-stage studies shaping the evidence base.

Development programme
CLINICALTRIALS.GOV · LIVE REGISTRY
190
registered trials across all phases
LATEST COMPLETION 2026
47
Active studies
33
Recruiting
87
Late-stage (III+)
85
Completed
58
Discontinued
PHASE DISTRIBUTIONn = 190
Early Phase 19Phase 115Phase 1 / 27Phase 272Phase 2 / 312Phase 336Phase 416Phase N / A23

Late-stage studies

Phase III+ trials still open or recently active — where late-stage evidence is being generated.

Clinical Trial of Androgen Effects on the Reproductive Neuroendocrine Axis

WithdrawnPH IVUniversity of California, San Diego2028

Letrozole for Treatment of Uterine Fibroids: A Randomized, Placebo-Controlled Trial

RecruitingPH IVUniversity of California, San Franciscon=1402028

Use of Letrozole in the Treatment of Early Ectopic Pregnancy

RecruitingPH IVHospital de Clinicas de Porto Alegren=1302026

Randomized Controlled Trial of Combined Letrozole and Clomid (CLC II) Versus Letrozole Alone for Women With Anovulation

Active, not recruitingPH IVRachel Mejian=1902025

An Investigator Initiated Registry of Simple Oral Therapy for Low Risk Breast Cancer (SOLR)

WithdrawnPH IVFred Hutchinson Cancer Center2025

Recent completions

Trials that read out recently, adding to the completed evidence base.

ONO-4578-06: Phase I , Open-label, Non-blind, First-line Endocrine Therapy With ONO-4578 and Standard Treatment Letrozole and CDK4/6 Inhibitors (Palbociclib or Abemaciclib) in Patients With Metastatic or Recurrent Postmenopausal Hormone Receptor-positive HER2-negative Breast Cancer

CompletedPH IOno Pharmaceutical Co., Ltd.n=462026

Sodium-Glucose Co-Transporter-2 Inhibitors as Adjuvant Therapy With Letrozole in Induction of Ovulation in Women With Polycystic Ovarian Syndrome

CompletedPH IIIBeni-Suef Universityn=2002026

Comparative Evaluation of the Efficacy of Letrozole, L-Carnitine, and Their Combination on Sperm Quality, Oxidative Stress, and ART Outcomes in Men With Idiopathic Oligoasthenoteratozoospermia: A Three-Arm Randomized Clinical Trial.

CompletedPH II/IIITehran University of Medical Sciencesn=902026

Comparison of Letrozole Versus Danazole for Pain Management of Female Presenting With Endometriosis

CompletedPH IISidra Salmann=602025

AN INTERVENTIONAL, OPEN-LABEL, RANDOMIZED, MULTICENTER, PHASE 2 STUDY OF PF-07220060 PLUS LETROZOLE COMPARED TO LETROZOLE ALONE IN POSTMENOPAUSAL WOMEN 18 YEARS OR OLDER WITH HORMONE RECEPTOR-POSITIVE, HER2-NEGATIVE BREAST CANCER IN THE NEOADJUVANT SETTING

CompletedPH IIPfizern=1212025

Pre-Surgical Trial of Letrozole in Post-Menopausal Patients With Operable Hormone-Sensitive Breast Cancer

CompletedPH IIUniversity of Texas Southwestern Medical Centern=612025

Research activity

10 papers

Key research shaping understanding of this drug, combining the latest publications with the most influential evidence.

Publications over time
20072024
Most influential

Palbociclib and Letrozole in Advanced Breast Cancer.

The New England journal of medicine · 2016 · 2,179 cites

Ribociclib as First-Line Therapy for HR-Positive, Advanced Breast Cancer.

The New England journal of medicine · 2016 · 1,477 cites

Extending Aromatase-Inhibitor Adjuvant Therapy to 10 Years.

The New England journal of medicine · 2016 · 466 cites

Letrozole versus clomiphene for infertility in the polycystic ovary syndrome.

The New England journal of medicine · 2014 · 371 cites

Abemaciclib plus a nonsteroidal aromatase inhibitor as initial therapy for HR+, HER2- advanced breast cancer: final overall survival results of MONARCH 3.

Annals of oncology : official journal of the European Society for Medical Oncology · 2024 · 161 cites

Clinical considerations of the role of palbociclib in the management of advanced breast cancer patients with and without visceral metastases.

Annals of oncology : official journal of the European Society for Medical Oncology · 2018 · 73 cites
Recent papers

Abemaciclib plus a nonsteroidal aromatase inhibitor as initial therapy for HR+, HER2- advanced breast cancer: final overall survival results of MONARCH 3.

Annals of oncology : official journal of the European Society for Medical Oncology · 2024 · 161 cites

Chronic Aromatase Inhibition Attenuates Synaptic Plasticity in Ovariectomized Mice.

eNeuro · 2024 · 1 cites

Efficacy, safety, and biomarker analysis of nivolumab in combination with abemaciclib plus endocrine therapy in patients with HR-positive HER2-negative metastatic breast cancer: a phase II study (WJOG11418B NEWFLAME trial).

Journal for immunotherapy of cancer · 2023 · 48 cites

Clinical considerations of the role of palbociclib in the management of advanced breast cancer patients with and without visceral metastases.

Annals of oncology : official journal of the European Society for Medical Oncology · 2018 · 73 cites

A Phase II Clinical Trial of an Aromatase Inhibitor for Postmenopausal Women with Lymphangioleiomyomatosis.

Annals of the American Thoracic Society · 2017 · 26 cites

Palbociclib and Letrozole in Advanced Breast Cancer.

The New England journal of medicine · 2016 · 2,179 cites
Major research themes8
Aromatase Inhibitors2Breast Neoplasms2Letrozole2Aminopyridines1Antineoplastic Combined Chemotherapy Protocols1Benzimidazoles1Neuronal Plasticity1Ovariectomy1
Journals, researchers & institutions
Top journals
  • The New England journal of medicine4
  • Annals of oncology : official journal of the European Society for Medical Oncology2
  • Annals of the American Thoracic Society1
  • Breast cancer research and treatment1
  • eNeuro1
  • Journal for immunotherapy of cancer1
Leading researchers
  • Campone M2
  • Diéras V2
  • Finn RS2
  • Gelmon K2
  • Im SA2
  • Iwata H2
  • Lu DR2
  • Martin M2
Leading institutions
free-text, unnormalised
  • Mayo Clinic2
  • 3 Swedish Medical Center1
  • 9 Stanford University1
  • Abramson Cancer Center1
  • Advanced Cancer Translational Research Institute1
  • Aichi Cancer Center1

Related diseases

1 conditions

Regulator-approved indications and conditions co-mentioned with this drug across the research literature. Number shows shared papers.

Active research areas
Breast Neoplasms3

Related drugs

5 matches

Drugs sharing diseases, protein targets and literature with this one. Ranked by graph evidence (shared targets + diseases weighted above co-mentions).

Anastrozole

Acts on the same molecular target as Letrozole, with an overlapping disease area.

Shared target1 shared disease1 shared paper
Clomiphene

Studied across 2 of the same disease areas as Letrozole in the shared literature.

2 shared diseases1 shared paper
Abemaciclib

Studied across the same disease area as Letrozole in the shared literature.

1 shared disease2 shared papers
Palbociclib

Studied across the same disease area as Letrozole in the shared literature.

1 shared disease2 shared papers
Ribociclib

Studied across the same disease area as Letrozole in the shared literature.

1 shared disease1 shared paper
References & data sources
  • RxNorm (U.S. National Library of Medicine) — drug identity
  • ChEMBL (EMBL-EBI) & UniProt — pharmacology and targets
  • Europe PMC — research literature
  • ClinicalTrials.gov — clinical trials