Letrozole is a non-steroidal triazole aromatase inhibitor — the most potent of the third-generation AIs (IC50 ~2 nM, approximately 5× more potent than anastrozole). Reversibly inhibits CYP19A1 by coordinating the triazole nitrogen to the haem iron of the enzyme. Suppresses oestradiol >99% at standard doses in postmenopausal women. Greater oestrogen suppression than anastrozole makes it the reference compound for maximal oestrogen depletion research.
Also Known As
Femara, CGS 20267
Compound Class
Non-steroidal aromatase inhibitor (type II AI)
Molecular Formula
C₁₇H₁₁N₅
Molecular Weight
285.30 Da
CAS Number
112809-51-5
Half-Life
~2 days
Research Applications
Maximal Aromatase Inhibition Research
Letrozole achieves greater oestradiol suppression than anastrozole at standard doses. Used as reference when maximum CYP19A1 inhibition is the research endpoint. FEMTA assay, aromatisation rate studies in adipose tissue, and dose-response modelling.
ER-Positive Breast Cancer Research
BIG 1-98 trial: letrozole vs tamoxifen in postmenopausal ER+ BC — letrozole superior DFS. MA.17 trial: extended letrozole after 5 years tamoxifen. Definitive data set for third-generation AI in breast cancer research.
Fertility Research — Ovulation Induction
Off-label use: letrozole has become the preferred ovulation induction agent in PCOS, replacing clomiphene in many protocols. Transient oestrogen suppression triggers FSH surge without prolonged ER depletion. PCOS, anovulation, and luteal phase defect research models.
Male Infertility Research
Oestrogen suppression in men with elevated E2:T ratio — letrozole raises testosterone via reduced negative feedback. Relevant in obese male research models where peripheral aromatisation is high.
Key Research Data
Study / Source
Key Findings
BIG 1-98 Trial 2005 NEJM
N=8,028: letrozole vs tamoxifen postmenopausal ER+ BC — letrozole superior DFS, definitive third-gen AI vs SERM comparison
MA.17 Trial 2003 NEJM
Extended letrozole 5 years post-tamoxifen — 43% DFS improvement, established extended AI therapy model
Legro et al. 2014 NEJM (PCOS)
Letrozole vs clomiphene for ovulation in PCOS: letrozole superior live birth rates, now preferred agent
Specifications
Format
Oral tablet — 2.5mg per tablet
Purity
≥99% HPLC
Identity
MS confirmed
Storage
Room temperature
Potency vs anastrozole
~5× more potent CYP19A1 inhibition
Frequently Asked Questions
What is Letrozole (Femara)?
Letrozole (Femara) is a Non-steroidal aromatase inhibitor (type II AI). Letrozole is a non-steroidal triazole aromatase inhibitor — the most potent of the third-generation AIs (IC50 ~2 nM, approximately 5× more potent than anastrozole). Reversibly inhibits CYP19A1 by coordinating the triazole nitrogen to the haem iron of…
How does Letrozole work in research models?
Letrozole achieves greater oestradiol suppression than anastrozole at standard doses. Used as reference when maximum CYP19A1 inhibition is the research endpoint. FEMTA assay, aromatisation rate studies in adipose tissue, and dose-response modelling….
What makes Letrozole different from similar compounds?
BIG 1-98 trial: letrozole vs tamoxifen in postmenopausal ER+ BC — letrozole superior DFS. MA.17 trial: extended letrozole after 5 years tamoxifen. Definitive data set for third-generation AI in breast cancer research….
Does QSC ship Letrozole to the USA?
Yes. QSC Letrozole ships domestically across the USA and internationally to EU, UK, Canada, and Australia. Every batch carries a Janoshik third-party COA confirming ≥99% HPLC purity and MS identity verification.
