Last reviewed 2026-04-23 · How we verify

Letrozole Oral Tablet

Letrozole inhibits aromatase, the enzyme responsible for converting androgens to estrogen in postmenopausal women, thereby reducing circulating estrogen levels.

Letrozole inhibits aromatase, the enzyme responsible for converting androgens to estrogen in postmenopausal women, thereby reducing circulating estrogen levels. Used for Metastatic breast cancer in postmenopausal women, Adjuvant treatment of early-stage breast cancer in postmenopausal women, Extended adjuvant therapy following tamoxifen in postmenopausal women.

At a glance

Mechanism of action

Letrozole is a non-steroidal aromatase inhibitor that selectively blocks the cytochrome P450 enzyme aromatase, which catalyzes the final step of estrogen biosynthesis. By reducing estrogen levels, it suppresses the growth of estrogen-dependent breast cancer cells. This mechanism is particularly effective in postmenopausal women where aromatase is the primary source of estrogen production.

Approved indications

• Metastatic breast cancer in postmenopausal women
• Adjuvant treatment of early-stage breast cancer in postmenopausal women
• Extended adjuvant therapy following tamoxifen in postmenopausal women

Common side effects

• Hot flashes
• Arthralgia/joint pain
• Fatigue
• Headache
• Nausea
• Osteoporosis/bone loss
• Elevated cholesterol

Key clinical trials

• A Study of Elacestrant Versus Standard Endocrine Therapy in Women and Men With ER+,HER2-, Early Breast Cancer With High Risk of Recurrence (PHASE3)
• A Phase III Trial Comparing HRS-8080 With Standard Endocrine Therapy in Patients With High-Risk Early Breast Cancer (PHASE3)
• BGB-43395 Alone or as Part of Combination Therapies in Participants With Breast Cancer and Other Advanced Solid Tumors (PHASE1)
• A Study Evaluating the Efficacy and Safety of Multiple Treatment Combinations in Patients With Metastatic or Locally Advanced Breast Cancer (PHASE1, PHASE2)
• Refining Fertility-sparing Treatment in Endometrial Carcinoma Based on Molecular Classification (PHASE2, PHASE3)
• A Study of MK-5684 in People With Certain Solid Tumors (MK-5684-015/OMAHA-015) (PHASE2)
• A Study to Evaluate the Efficacy and Safety of Inavolisib in Combination With Phesgo Versus Placebo in Combination With Phesgo in Participants With PIK3CA-Mutated HER2-Positive Locally Advanced or Metastatic Breast Cancer (PHASE3)
• A Study of HRS-6208 in Combination With HRS-8080, or Fulvestrant, or Letrozole, With or Without HRS-6209 in Patients With Advanced Unresectable or Metastatic Breast Cancer (PHASE1, PHASE2)

Primary sources

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