Multinational trial of interrupting endocrine therapy to attempt pregnancy after breast cancer

Prospective data on the risk of recurrence among women with hormone receptor-positive early breast cancer who temporarily discontinue endocrine therapy to attempt pregnancy are lacking. The multinational POSITIVE trial included women aged 42 year or younger who interrupted adjuvant endocrine therapy after they had received adjuvant endocrine therapy for HR-positive EBC for 18 to 30 months, and desired pregnancy. After 1638 patient-years of follow-up, among 497 women, 368 (74.0%) had at least one pregnancy and 317 (63.8%) had at least one live birth (365 babies were born). The 3-year incidence of breast cancer events was 8.9%, compared with 9.2% in a control cohort of women who did not interrupt endocrine therapy but would have met the entry criteria for POSITIVE. The authors conclude that temporary interruption of endocrine therapy to attempt pregnancy was not associated with greater short-term risk of breast cancer events, although further follow-up is critical to inform longer-term safety.