Author: Prof. Dr. med. Peter Altmeyer

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Last updated on: 31.08.2022

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CAS number: 112809-51-5; (e) Letrozole

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Letrozole (molecular formula: C17H11N5) is an active substance from the group of non-steroidal aromatase inhibitors. By blocking the aromatases, the remaining oestrogen production in and after menopause decreases significantly. In addition, letrozole directly inhibits the aromatase in the tumour cells, thus limiting the growth and spread of the tumour cells.

Letrozole has no gestagenic, androgenic or estrogenic effect. The effect and strength of the preparation is similar to that of anastrozole.

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Advanced or metastatic breast cancer in postmenopausal patients

Undesirable effects
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Hot flashes and flushesFatigue




Sleep disturbances

worsening of cholesterol levels


Rare skin changes: vasculitides, non-specific dermatitides, erythema nodosum, subacute cutaneous lupus erythematosus (see below aromatase inhibitors)

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The active ingredient was placed on the Prohibited List by the World Anti-Doping Agency (WADA) in 2008. Possession of more than 75 mg is classified as "not small quantity" under the German Medicines Act, in accordance with the Doping Drug Quantity Ordinance.

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  1. Mamounas EP et al (2019) Use of letrozole after aromatase inhibitor-based therapy in postmenopausal breast cancer (NRG Oncology/NSABP B-42): a randomised, double-blind, placebo-controlled, phase 3 trial. Lancet Oncol 20: 88-99.
  2. Rugo HS et al (2019) Palbociclib plus letrozole as first-line therapy in estrogen receptor positive/human epidermal growth factor receptor 2-negative advanced breast cancer with extended follow-up. Breast Cancer Res Treat 174:719-729.


Last updated on: 31.08.2022