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Breastfeeding is feasible among young breast cancer survivors, including BRCA carriers, and is mostly performed in the contralateral breast. Breastfeeding does not increase the risk for breast cancer recurrence. These were the main findings of the POSITIVE trial and the BRCA BCY cohort study.

Young breast cancer survivors face significant challenges, including fertility issues. Recently, the prospective, single-arm POSITIVE trial (NCT02308085) showed that for women with HR+ breast cancer, temporary interruption of adjuvant endocrine therapy to attempt pregnancy is safe and does not confer a greater short-term risk for breast cancer events¹.

The trial enrolled 518 participants with HR+ stage I–III breast cancer wishing to become pregnant. Participants stopped endocrine therapy for up to 2 years to allow conception, delivery, and (optional) breastfeeding. Fedro Peccatori, MD, PhD, from the European Institute of Oncology, in Italy presented results on breastfeeding feasibility and safety outcomes, a secondary endpoint of the POSITIVE study².

Of 313 participants who did not have a bilateral mastectomy, 196 (62%) started breastfeeding after delivery (83.6% nullipara). Most mothers breastfed from the contralateral breast only (69.2%), 29.2% breastfed from both breasts, and 1.5% breastfed from the affected breast. Factors associated with a greater proportion of breastfeeding were breast-conserving therapy, age older than 35 years, nulliparity, and enrolment in Asia, Pacific, or the Middle East. Breastfeeding was not associated with any new breast cancer events up to 41 months of follow-up (event rates of 3.6% in women who breastfed vs 3.1% in women who did not breastfeed).

Similar results were obtained in an international retrospective cohort study (BRCA BCY Collaboration [NCT03673306]), presented by Eva Blondeaux, MD, from the University of Genova, in Italy^3.4. No increased risk for breast cancer events (locoregional or contralateral recurrence) was observed in BRCA carriers who breastfed after delivery (n=110) versus BRCA carriers who did not breastfeed (n=68). The 7-year cumulative incidence of breast cancer events was 29% in the breastfeeding group and 37% in the non-breastfeeding group (HR 1.08; 95% CI 0.57–2.06; P=0.818). In addition, no difference was observed in both disease-free and overall survival.

In conclusion, breastfeeding is feasible among young breast cancer survivors, including BRCA carriers, and is mostly performed in the contralateral breast. Breastfeeding does not increase the risk for breast cancer recurrence.

Medical writing support was provided by Marten Dooper.
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