Patients with breast cancer who pause their endocrine therapy to try to get pregnant experienced short-term rates of breast cancer recurrence similar to women who do not pause therapy for pregnancy, according to results from the POSITIVE clinical trial.

Many young breast cancer survivors desire pregnancy. However, standard 5-10 years of adjuvant endocrine therapy compromises conception in women with hormone-positive disease. Although retrospective evidence shows that pregnancy after breast cancer does not worsen the disease outcome, regardless of hormone receptor status, women are often discouraged to get pregnant after breast cancer.1

The POSITIVE trial prospectively evaluated outcomes of pregnancy after breast cancer and interruption of endocrine therapy to attempt pregnancy. The study enrolled 518 women (≤42 years) who had at least 18 and no more than 30 months of endocrine therapy for stage I-III HR-positive breast cancer and who desired to become pregnant. After enrolment, women had up to 2 years to attempt pregnancy, conceive, and breastfeed, including a 3-month washout period. Endocrine therapy resumption was strongly recommended after pregnancy to complete 5-10 years. The primary endpoint was breast cancer-free interval (BCFI). A cohort of 1,499 SOFT/TEXT patients was used as external control.2 Dr. Ann Partridge (Dana-Farber Cancer Institute) presented the results3 at the 2022 San Antonio Breast Cancer Symposium.

The median time from breast cancer diagnosis to enrolment was 29 months, and the median follow-up from enrolment was 41 months.4 Cumulative incidence of both breast cancer-free and distant relapse-free interval (DRFI) events at 3 years of follow-up was not statistically different in POSITIVE versus SOFT/TEXT: 8.9% versus 9.2% (BCFI) and 4.5% versus 5.8% (DRFI), respectively. In addition, no difference was observed in BCFI between women in the POSITIVE trial who became pregnant compared with women who did not become pregnant.

Of 497 women followed for pregnancy status, 368 (74.0%) had at least one pregnancy and 317 (63.8%) had at least one live birth, with a total of 365 babies (15 sets of twins) born. Birth defects were low (2%) and not clearly associated with treatment exposure. At 48 months, 8% of patients had cancer recurrence or death before resuming endocrine therapy, 76% had resumed endocrine therapy, and 15% had not (yet) resumed endocrine therapy.

Based on these results, Dr. Partridge concluded that “temporary interruption of endocrine therapy to attempt pregnancy among women who desire pregnancy does not impact short-term disease outcomes. These data stress the need to incorporate patient-centred reproductive healthcare in the treatment and follow-up of young women with breast cancer.”

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