Is breast cancer risk the same for all progestogens?

Area of Science:

• Reproductive Endocrinology
• Oncology
• Epidemiology

Background:

• The CECILE study, a population-based case-control investigation, examined 1,555 postmenopausal women to assess the relationship between menopausal hormone therapy (MHT) products and breast cancer (BC) risk.
• Participants included 739 incident BC cases and 816 controls, with data collected via questionnaires and pathology reports.

Discussion:

• While overall MHT use (estrogen-only therapy [ET], estrogen combined with progestin therapy [EPT], tibolone) was not linked to increased BC risk, current EPT use for 4+ years showed a significant association.
• Specifically, EPT containing synthetic progestogens, but not micronized progesterone, was associated with a significantly increased BC risk.
• MHT initiated within one year of menopause onset (early EPT) was linked to higher BC risk, whereas later initiation showed no increased risk.

Key Insights:

• Estrogen-only therapy (ET) and EPT with natural progesterone do not appear to elevate breast cancer risk.
• Tibolone and EPT containing synthetic progestogens are associated with increased breast cancer risk.
• Initiating MHT, particularly EPT with synthetic progestogens, early in menopause (within 1 year) is linked to a higher risk compared to delayed initiation.

Outlook:

• Further research is warranted to elucidate the specific mechanisms by which synthetic progestogens in EPT influence breast cancer development.
• Clinical guidelines may need to consider the type of progestogen and timing of initiation when prescribing MHT to mitigate breast cancer risk.
• Long-term follow-up studies are crucial to confirm these findings and assess the cumulative risk associated with different MHT regimens.