Recent POSITIVE Trial Reveals No Breast Cancer Events in Breastfeeding Patients

Recent findings from the POSITIVE trial indicate that women who breastfeed after undergoing endocrine therapy for hormone receptor-positive (HR+) breast cancer do not face an increased risk of breast cancer events. This research, published in the *Journal of Clinical Oncology* on July 9, 2025, provides significant insights for breast cancer survivors considering breastfeeding following treatment.

The POSITIVE trial, which stands for Positive Pregnancy Intentions Study, aimed to assess whether patients with HR+ breast cancer could safely interrupt their endocrine therapy to conceive and breastfeed. The study involved 497 women diagnosed with stage I to II HR+ breast cancer, all aged 42 or younger. Participants were allowed to pause their endocrine therapy for a maximum of two years to facilitate pregnancy and breastfeeding, after which they were encouraged to resume treatment as per established guidelines.

The latest findings revealed that there was no statistically significant difference in the cumulative incidence of breast cancer-related events between women who breastfed for four months or longer and those who did not. Specifically, the twelve-month estimates of the breast cancer-free interval (BCFI) were 1.1% for breastfeeding women compared to 1.9% for non-breastfeeding women. At the 24-month mark, the rates stood at 3.6% and 3.1%, respectively, demonstrating an absolute difference of just 0.4% (95% CI, –4.3% to 5.2%) between the two groups.

Dr. Fedro A. Peccatori, a medical oncologist at the European Institute of Oncology in Milan, Italy, and co-author of the study, stated, “With the limitations that the trial had a highly motivated patient and health care provider population, we found that most women who gave birth in the POSITIVE study were able to breastfeed, and that those who underwent breast-conserving surgery predominantly breastfed from the contralateral breast.” The follow-up period averaged 22 months from the first live birth, with a total of nine breast cancer events recorded in six of the 196 women who breastfed compared to three events in 117 non-breastfeeding participants.

The trial revealed that 62.6% of patients breastfed their first child, with breastfeeding rates significantly higher among women who underwent breast-conserving surgery (77.8%) compared to those who had not (45.2%). Additionally, cultural factors appeared to influence breastfeeding rates, with a higher frequency reported among women from Asian/Pacific/Middle Eastern backgrounds (85.7%) compared to their European and North American counterparts.

Dr. Anna H. Partridge, a prominent figure in breast cancer research and vice chair of Medical Oncology at Dana-Farber Cancer Institute, expressed optimism about the trial's implications: “I think POSITIVE will open the door for more young women to say, ‘I can take a break and try to become pregnant’. At least in the short term, it appears safe. Hopefully, in the long term, we’ll have data that appear safe from a prospective standpoint.”

As the POSITIVE trial continues to generate interest, the results are expected to encourage more young women diagnosed with HR+ breast cancer to consider pregnancy and breastfeeding without fear of adversely affecting their health. With the growing body of evidence supporting safe practices for pregnant and breastfeeding women in this demographic, healthcare providers are urged to engage in discussions that empower patients with knowledge and options.

The results of this study build on previous findings presented at the 2024 European Society for Medical Oncology Congress, further solidifying the role of informed decision-making in patient care. The importance of ongoing research in this area cannot be overstated, as it addresses a critical gap in the understanding of reproductive health among breast cancer survivors. With more studies anticipated, the future looks promising for integrating family planning into breast cancer treatment protocols.