What is the role of endocrine therapy (e.g. tamoxifen) in breast cancer?

Endocrine therapy is used for oestrogen-receptor (ER)-positive breast cancers to block oestrogen's growth-promoting effect.

Tamoxifen (a SERM) is used in pre- and post-menopausal women; aromatase inhibitors are used in postmenopausal women. Adjuvant endocrine therapy is given for 5 years (now often extended to 10), substantially reducing recurrence and mortality.

Clinical relevance. Endocrine therapy (tamoxifen/aromatase inhibitors) substantially reduces recurrence and mortality in ER-positive breast cancer.

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Endocrine therapy in breast cancer

Endocrine therapy is a cornerstone of treatment for ER-positive breast cancer.

Rationale

• ER-positive tumours depend on oestrogen for growth - blocking this is effective.

Tamoxifen

• A selective oestrogen receptor modulator (SERM) that blocks the oestrogen receptor in breast tissue.
• Used in both pre- and postmenopausal women.

Aromatase inhibitors

• (e.g. anastrozole, letrozole) - reduce oestrogen production; used in postmenopausal women (ineffective alone premenopausally).

Duration and benefit

• Adjuvant endocrine therapy is given for at least 5 years, now often extended to 10 years in higher-risk cases.
• Substantially reduces recurrence and mortality in ER-positive disease.

Note

• Tamoxifen side effects include hot flushes, venous thromboembolism, and a small increased risk of endometrial cancer; aromatase inhibitors cause arthralgia and bone loss.