# Letrozole (and other aromatase inhibitors)

Source: https://onco.cc/drugs/letrozole/  
OnCo record `letrozole` (Treatment). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Daily pills that stop the body making oestrogen after menopause, the backbone of hormone therapy for most breast cancers.

## Summary

Non-steroidal (letrozole, anastrozole) and steroidal (exemestane) aromatase inhibitors block conversion of androgens to oestrogens in fat and tumour tissue. Superior to tamoxifen for postmenopausal women in adjuvant (ATAC, BIG 1-98) and metastatic settings; the standard partner for CDK4/6 inhibitors in first-line metastatic disease. Used with ovarian suppression in premenopausal women (SOFT/TEXT). Arthralgia, bone loss, and vaginal dryness drive non-adherence.

## Fields

- Kind: Treatment
- Status: approved
- Last checked: 2026-09-07
- Brand: Femara; anastrozole (Arimidex); exemestane (Aromasin)
- Modality: Small-molecule aromatase inhibitor
- Mechanism: Competitive (letrozole, anastrozole) or irreversible (exemestane) inhibition of CYP19A1 aromatase.
- Approvals: US 1997: Advanced breast cancer after tamoxifen (letrozole); US 2005: Adjuvant early breast cancer (letrozole)
- Dosing: Oral; Letrozole 2.5 mg, anastrozole 1 mg, or exemestane 25 mg once daily; 5-10 years adjuvant; until progression metastatic

## Notes

- In low-grade serous ovarian cancer, retrospective series and the NRG-GY019 trial support endocrine maintenance, and letrozole is now widely used after surgery or chemotherapy in LGSOC and in ER-positive endometrial cancer, often with palbociclib or abemaciclib; it is cheap and well tolerated, with bone loss and arthralgia the main issues.

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Letrozole
- FDA label (DailyMed): https://dailymed.nlm.nih.gov/dailymed/search.cfm?query=Letrozole

## Connected records

- cancers: [Adult granulosa cell tumour of the ovary](https://onco.cc/cancers/granulosa-cell-tumour/), [Advanced or recurrent endometrial cancer](https://onco.cc/cancers/advanced-recurrent-endometrial-cancer/), [Endometrial cancer](https://onco.cc/cancers/endometrial/), [Endometrial cancer with no specific molecular profile](https://onco.cc/cancers/endometrial-nsmp/), [High-risk early HR-positive breast cancer](https://onco.cc/cancers/hr-positive-early-high-risk/), [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/), [Inflammatory breast cancer](https://onco.cc/cancers/inflammatory-breast-cancer/), [Invasive lobular carcinoma of the breast](https://onco.cc/cancers/invasive-lobular-carcinoma/), [Leiomyosarcoma](https://onco.cc/cancers/leiomyosarcoma/), [Low-grade serous ovarian cancer](https://onco.cc/cancers/low-grade-serous-ovarian-cancer/), [Male breast cancer](https://onco.cc/cancers/male-breast-cancer/), [Mucinous carcinoma of the breast](https://onco.cc/cancers/mucinous-carcinoma-breast/), [Ovarian cancer](https://onco.cc/cancers/ovarian/), [Platinum-resistant ovarian cancer](https://onco.cc/cancers/platinum-resistant-ovarian-cancer/), [Tubular carcinoma of the breast](https://onco.cc/cancers/tubular-carcinoma-breast/), [Uterine sarcoma](https://onco.cc/cancers/uterine-sarcoma/)
- technologies: [Acupuncture for aromatase-inhibitor joint pain](https://onco.cc/technologies/acupuncture-aromatase-inhibitor-arthralgia/), [Acupuncture for hot flushes on endocrine therapy](https://onco.cc/technologies/acupuncture-hot-flushes/), [Antiandrogens for hair: spironolactone, finasteride, dutasteride](https://onco.cc/technologies/hair-antiandrogens-alopecia/), [Bone loss caused by cancer treatment, and what rebuilds it](https://onco.cc/technologies/cancer-treatment-bone-loss/), [Dietitian-led weight-loss programmes in HR-positive breast cancer](https://onco.cc/technologies/dietitian-led-weight-loss-breast/), [Endocrine therapy (SERMs, AIs, SERDs)](https://onco.cc/technologies/endocrine-therapy/), [FES PET (oestrogen receptor imaging)](https://onco.cc/technologies/fes-pet/), [Menopause brought on by cancer treatment, and the options for it](https://onco.cc/technologies/menopause-after-cancer-treatment/), [Minoxidil for persistent chemotherapy- and endocrine-therapy hair loss](https://onco.cc/technologies/minoxidil-chemotherapy-alopecia/), [Vaginal oestrogen after breast cancer: what the evidence says, and where it disagrees](https://onco.cc/technologies/vaginal-oestrogen-after-breast-cancer/)
- targets: [Aromatase (CYP19A1)](https://onco.cc/targets/aromatase/), [Estrogen receptor (ERα)](https://onco.cc/targets/estrogen-receptor/)
- companies: [Novartis](https://onco.cc/companies/novartis/)
- pathways: [Breast cancer (KEGG map)](https://onco.cc/pathways/breast-cancer-signalling/), [Chemical carcinogenesis - receptor activation](https://onco.cc/pathways/chemical-carcinogenesis-receptor-activation/), [Endometrial cancer (KEGG map)](https://onco.cc/pathways/endometrial-cancer-signalling/), [Oestrogen receptor signalling](https://onco.cc/pathways/er-signaling/)
- terms: [Aromatase inhibitor](https://onco.cc/terms/aromatase-inhibitor/), [Endocrine-therapy-induced alopecia](https://onco.cc/terms/alopecia-endocrine-therapy/), [Low-grade serous ovarian cancer (LGSOC)](https://onco.cc/terms/lgsoc/)
- trials: [A Study of Avutometinib (VS-6766) + Defactinib (VS-6063) in Recurrent Low-Grade Serous Ovarian Cancer](https://onco.cc/trials/nct06072781/), [COMET (Comparison of Operative versus Monitoring and Endocrine Therapy)](https://onco.cc/trials/comet-dcis/), [HOBOE: A Phase 3 Study of Adjuvant Triptorelin and Tamoxifen, Letrozole, or Letrozole and Zoledronic Acid in Premenopausal Patients With Breast Cancer](https://onco.cc/trials/nct00412022/), [MONALEESA-2](https://onco.cc/trials/monaleesa-2/), [MONARCH 3](https://onco.cc/trials/monarch-3/), [PALOMA-2](https://onco.cc/trials/paloma-2/), [PATINA](https://onco.cc/trials/patina/), [PF-07104091 as a Single Agent and in Combination Therapy](https://onco.cc/trials/nct04553133/), [SOFT & TEXT](https://onco.cc/trials/soft-text/), [Study of AVZO-021 in Patients With Advanced Solid Tumors](https://onco.cc/trials/nct05867251/), [Study of GVV858 as a Single Agent or in Combination With Endocrine Therapy in Patients With HR+/HER2- Breast Cancer and Other Advanced Solid Tumors](https://onco.cc/trials/nct07288359/), [Study of PF-07248144 in Advanced or Metastatic Solid Tumors](https://onco.cc/trials/nct04606446/), [Study to Test the Safety and Tolerability of PF-07220060 in Participants With Advance Solid Tumors](https://onco.cc/trials/nct04557449/)
- people: [Wendy Parulekar](https://onco.cc/people/parulekar-wendy/)
- ideas: [GLP-1 receptor agonists as adjuvant weight-loss therapy in HR-positive breast cancer](https://onco.cc/ideas/idea-nl-glp1-adjuvant-hr-breast/), [Pool purchasing of essential cancer medicines across countries](https://onco.cc/ideas/idea-cost-pooled-procurement-essential/), [Transparent cost-plus pricing for every oral oncology generic](https://onco.cc/ideas/idea-cost-transparent-generic-pricing/)
- drugs: [Aminoglutethimide](https://onco.cc/drugs/aminoglutethimide/), [Anastrozole](https://onco.cc/drugs/anastrozole/)
- biomarkers: [ER status (oestrogen receptor by IHC)](https://onco.cc/biomarkers/er-status/), [PR status (progesterone receptor by IHC)](https://onco.cc/biomarkers/pr-status/)
- roadmaps: [Hormonal therapy roadmap: removing the ovaries → tamoxifen → oral degraders switched by a blood test](https://onco.cc/roadmaps/hormonal-therapy-roadmap/)

---
JSON: https://onco.cc/api/v1/entities/letrozole.json