Reduced Breast Cancer Risk in Women With A History of Pre-Eclampsia: Implications of Postmenopausal Hormone Therapy.

Abstract

Both prior pre-eclamptic pregnancy and menopausal hormone therapy (MHT) are determinants for breast cancer (BC). To study the effects of prior pre-eclampsia and MHT use on BC risk. Register-based cohort study with follow-up for BC (Finnish Cancer Register 1987-2023) and MHT use (National Reimbursement Register 1994-2019). Nationwide population-based study in Finland. Women with prior pre-eclampsia (n = 31 688) and age-matched control women without pre-eclampsia (n = 91 726) who had given birth in 1969-1993. The BC risks were compared between prior pre-eclamptic and control women and between prior pre-eclamptic MHT users and non-users. Breast cancer occurred less frequently (p = 0.02) in prior pre-eclamptic women (6.6%, n = 2095) than in the controls (7.0%, n = 6410). The age-adjusted BC risk in prior pre-eclamptic women (aHR=0.89, 95% CI 0.83-0.94) was reduced. No clinical characteristics from pre-eclamptic pregnancy (e.g. severity) predicted the magnitude of the BC risk reduction.MHT use was accompanied with comparable BC risk rise in prior pre-eclamptic and control women (1.25, 1.12-1.40 vs. 1.30, 1.18-1.42). The increased risk with any MHT use was seen in both cohorts already after 5 years. This was primarily associated to estrogen-progestogen use, whereas estrogen only was not associated with BC risk in prior pre-eclamptic women. BC risk is reduced in women with a history of pre-eclampsia. The MHT-associated increase in BC risk is similar among women with or without a history of pre-eclampsia. Thus, pre-eclampsia is no contraindication for the use of MHT.