In a prospective study (POSITIVE) reported in the Journal of Clinical Oncology, Peccatori et al investigated breastfeeding patterns among women who had a live birth after treatment of hormone receptor–positive breast cancer.
Study Details
Between December 2014 and December 2019, 518 women who interrupted endocrine therapy to attempt pregnancy were recruited from sites in 20 countries. Eligible patients had stage I to III breast cancer, were aged 42 or younger at enrollment, and had received 18 to 30 months of endocrine therapy prior to enrollment. An earlier report from the study showed no increase in short-term risk for breast cancer events among women who interrupted endocrine therapy to attempt pregnancy.
Key Findings
At a median follow-up of 41 months, 317 of the 518 women had at least one live birth, with 313 being eligible for analysis. Among the 313 women included in the analysis, 196 (62.6%) breastfed. Among 167 women who had breast-conserving surgery, 130 (77.8%) breastfed, with 90 of the 130 women (69.2%) breastfeeding from the unaffected breast alone. Among 146 women who had unilateral mastectomy, 66 (45.2%) breastfed.
Overall, the incidence of breastfeeding was higher in women aged 35 and older vs younger age (67.6% vs 55.7%) and in those without vs with a previous live birth (66.4% vs 48.5%). A total of 103 of the 196 women (52.6%) who breastfed did so for more than 4 months (median = 4.4 months, 95% confidence interval [CI] = 4.0–5.3 months).
The cumulative incidence of breast cancer events at 24 months from first on-study live birth was 3.6% in the breastfeeding group vs 3.1% in the nonbreastfeeding group (0.5% difference, 95% CI = –4.3% to 5.2%).
The investigators concluded: “In POSITIVE, two thirds of women who gave birth after [breast cancer] diagnosis breastfed, mostly for 4 months or more. In early follow-up, we did not observe differences in [breast cancer]-related events in women who breastfed compared with those who did not. These results are key for women who wish to pursue pregnancy and breastfeeding after [breast cancer].”
Fedro A. Peccatori, PhD, MD, of the Fertility and Procreation Unit, Gynecologic Oncology Program, European Institute of Oncology IRCCS, Milan, Italy, is the corresponding author of the Journal of Clinical Oncology article.
Disclosure: The study was supported by the ETOP IBCSG Partners Foundation (globally) and the Alliance for Clinical Trials in Oncology (in North America), in collaboration with the Breast International Group (BIG), the BIG cooperative groups, and the National Clinical Trials Network of the National Cancer Institute. For full disclosures of all study authors, visit ascopubs.org.
