A 38-year-old woman is commenced on hormone replacement therapy (HRT) with continuous combined estradiol 2 mg + dydrogesterone 10 mg daily for perimenopausal symptoms. She had a 6-year history of taking a combined oral contraceptive pill (COC) in her 30s. She asks about her breast cancer risk with HRT. The MOST accurate evidence-based counseling point from the WHI and Million Women Study data is:

• A Combined estrogen-progestogen HRT increases breast cancer risk, while estrogen-only HRT does not increase risk (and may even reduce it in hysterectomized women) ✓
• B All forms of HRT have equal breast cancer risk; the risk is equivalent to one extra case per 1,000 women per year
• C Breast cancer risk with HRT is greater than with COC use, as postmenopausal breast tissue is more sensitive to exogenous hormones
• D Micronized progesterone (body-identical HRT) has equivalent breast cancer risk to synthetic progestogens in all cohort data

Explanation

The WHI trial (2002, 2004) and Million Women Study showed that combined estrogen-progestogen HRT is associated with increased breast cancer risk (approximately 8 extra cases per 10,000 women-years after 5 years of use). Critically, the WHI estrogen-only arm (in hysterectomized women) did not show increased breast cancer risk and some analyses suggested a non-significant reduction. This dichotomy is explained by the proliferative effect of progestogens on breast epithelium. French E3N cohort data suggest micronized progesterone (body-identical) may have a more favorable breast risk profile than synthetic progestogens (MPA, norethisterone) — option D overstates equivalence. COC use (option C) has a slight breast cancer risk increase which reverses within 10 years of stopping; direct comparison with HRT is complex but COC is typically used younger when baseline risk is lower.

Reference: Shaw's Textbook of Gynaecology, 17th ed.

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Written and medically reviewed by the StethoPrep medical team.