Breast cancer can occur in women below 50 years old and represents 25% of the total number of cases. Risk factors and histological characteristics of breast cancer are different in young women compared with older women. There are many publications on the risk of breast cancer and hormone treatment (MHT) in postmenopausal women. However, less is known about use of MHT in young women and especially looking separately at the impact of estrogen-only treatment (ET) and combined estrogen–progestin treatment (EPT). A recent study aimed to investigate whether the use of MHT is a risk factor for young-onset breast cancer . The authors used the Two Sister Study for this purpose. It is a sister-matched case–control study of young-onset breast cancer from the Sister Study, a prospective cohort study of 50,884 women without breast cancer who had a full or half sister who had been diagnosed with breast cancer; 1422 cases and 1689 controls were included. Because 10% of control sisters and no case sisters had reached the age of 50 years before 2002 when the WHI study was published and because MHT prescriptions decreased drastically thereafter, a propensity score was used to decrease the impact of this bias. Results show that a low percentage of women used MHT. The most frequent was ET (7% of controls and 4% of cases), then EPT (3% and 2%, respectively) and progestin alone (PT) (1% and 1%). Crude odds ratios (OR) for breast cancer were less than 1 for every MHT category except PT. ET use was inversely associated with young-onset breast cancer (propensity score, adjusted OR =0.58; 95% CI 0.34–0.99); the adjusted OR for EPT use was 0.80 (95% CI 0.41–1.59) and for PT was 1.51 (95% CI 0.76–3.00). Adjustment for duration of use, age at first use, menopausal status at first use, and recency of use did not appear to modify the association. There was no interaction by oophorectomy status but women using ET were more often hysterectomized and oophorectomized. The authors concluded that neither ET nor EPT increase the risk of young-onset breast cancer and that ET might be associated with a reduced risk.
Unité de Gynécologie Endocrinienne, Université Paris Descartes, APHP, Cochin Port Royal, Paris, France
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