Breastfeeding After Breast Cancer Proves Safe in Early Trial Results

Women with HR+ early breast cancer who paused endocrine therapy to become pregnant breastfed without increased risk of recurrence in the short term.

Women with hormone receptor–positive (HR-positive) early breast cancer who paused endocrine therapy to become pregnant were able to breastfeed without increased risk of recurrence in the short term, according to data from the POSITIVE trial shared in the Journal of Clinical Oncology.

The POSITIVE trial is a prospective international study which was designed to evaluate the safety of temporarily interrupting endocrine therapy so women could attempt pregnancy. Earlier findings showed no rise in short-term breast cancer events after treatment breaks. The most recent analyses focused on breastfeeding. Notably, this is an area where very little prospective data exist for women with a history of breast cancer.

Researchers examined breastfeeding frequency, duration and whether women nursed from the affected or unaffected breast. They also estimated the cumulative incidence of breast cancer events by breastfeeding status.

Notably, investigators who conducted the study shared previous findings from the POSITIVE trial in a 2024 ESMO Annals of Oncology journal article.

Breastfeeding Patterns After Breast Cancer Treatment

According to information shared, at a median follow-up of 41 months, 317 participants had at least one live birth. Of these, 313 were eligible for analysis, and 196 women (approximately 63%) breastfed a total of 232 babies. The majority of women who underwent breast-conserving surgery chose to breastfeed, most often from the unaffected breast. Notably, 90 of 130 women (69%) who had breast-conserving surgery nursed from only the contralateral side.

Among women who had a unilateral mastectomy, 66 of 146 (45%) breastfed. Additionally, 38 patients, or about 12%, breastfed from both breasts. Breastfeeding was more common in women older than 35 (67.6% compared with 55.7% in younger women) and in those without prior children (66.4% compared with 48.5%).

Over half of women who breastfed (103 of 196, 52.6%) continued for more than four months, with a median duration of 4.4 months. Neither the length of prior endocrine therapy nor the time from enrollment to first live birth influenced the likelihood or length of breastfeeding.

Does Breastfeeding Increase the Risk of Breast Cancer Coming Back?

Importantly, breastfeeding did not appear to affect breast cancer–related outcomes. At two years from the first live birth, the cumulative incidence of breast cancer events was 3.6% in the breastfeeding group and 3.1% in the non-breastfeeding group which represented a difference of 0.5%.

In total, nine breast cancer events were reported, including three local recurrences. When analyzed for breast cancer–free interval, the data indicated that there was no meaningful difference between women who breastfed and those who did not.

What Do These Breastfeeding Results Mean for Patients With Breast Cancer?

These results suggest that breastfeeding is feasible for many women who have paused endocrine therapy to pursue pregnancy, with most continuing for several months. In early follow-up, breastfeeding did not increase the risk of recurrence.

“Nearly two-thirds of women who gave birth after breast cancer diagnosis breastfed, many for four months or longer,” researchers reported in the 2024 ESMO Annals of Oncology. “In early follow-up, no impact on breast cancer events was observed."

Longer follow-up is still needed, but these findings show that for women with early HR-positive breast cancer who wish to breastfeed after treatment interruption, there is no significant association with breast cancer recurrence.

The investigators concluded their Journal of Clinical Oncology research by stating: “These results are key for women who wish to pursue pregnancy and breastfeeding after breast cancer.”

References

1. “Breastfeeding After Hormone Receptor–Positive Breast Cancer: Results From the POSITIVE Trial,” by Dr. Fedro A. Peccatori, et al. The Journal of Clinical Oncology; July 9, 2025.
2. “Breastfeeding in women with hormone receptor-positive breast cancer who conceived after temporary interruption of endocrine therapy: Results from the POSITIVE trial,” by H.A. Azim, Jr, et al. The ESMO Annals of Oncology; Sept 2024.

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