For many new mothers who have undergone breast cancer treatment, including those who harbour the BRCA gene mutation, breastfeeding appears to be a safe and viable option, posing no increased risk of recurrence or development of new breast cancers, according to new research.

Young BRCA carriers

In the first study, which involved young breast cancer survivors with a germline BRCA mutation (median age at index diagnosis 30 years), the cumulative incidence of locoregional and/or contralateral breast cancer events over a median follow-up of 7 years after delivery did not significantly differ between the participants who breastfed and those who did not (29 percent vs 37 percent; adjusted subhazard ratio [sHR], 1.08, 95 percent confidence interval [CI], 0.57?2.06; p=0.818). [ESMO Congress 2024, abstract 1815O]

The results were consistent in subgroup analyses defined by specific BRCA gene (BRCA1 vs BRCA2: p=0.840), pregnancy interval (≤5 vs >5 years: p=0.116), hormone receptor status (ER- and/or PR-negative vs ER- and PR-positive: p=0.768), and chemotherapy use (no vs yes: p=0.284).

Likewise, breastfeeding had no impact on either disease-free survival (DFS) (adjusted HR, 0.83, 95 percent CI, 0.49?1.41; p=0.492) or overall survival (OS) (number of OS events: 9 in the breastfeeding group vs 3 in the nonbreastfeeding group [8.2 percent vs 4.4 percent]).

First study author Dr Eva Blondeaux from the IRCCS Ospedale Policlinico San Martino in Genova, Italy, acknowledged that the small number of OS events prevented her team from making formal statistical comparison.

“Our study provides the first evidence on the safety of breastfeeding after breast cancer in young women carrying a germline BRCA mutation,” Blondeaux said. “Our findings emphasize the possibility of achieving a balance between maternal and infant needs without compromising oncological safety.”

The study enrolled 4,732 participants from 78 centres across 26 countries, among whom 659 conceived after a breast cancer diagnosis and 474 had a live birth. After delivery, 110 (23.2 percent) participants breastfed (median duration 5 months), 68 (14.4 percent) did not breastfeed, 225 (47.5 percent) underwent bilateral risk-reducing mastectomy before delivery and were thus unable to breastfeed, and 71 (15.0 percent) had unknown breastfeeding status.

Significantly more participants in the breastfeeding group than in the no breastfeeding group were nulliparous at the index diagnosis (61.8 percent vs 45.6 percent; p=0.026) and reported no history of smoking (71.8 percent vs 57.4 percent; p=0.019). Other patient characteristics as well as treatment patterns were similar between the two groups.

Women with HR+ breast cancer

Similar results were observed in a secondary analysis of the POSITIVE trial, which expanded the investigation beyond BRCA and included women with HR-positive early breast cancer who conceived after temporary interruption of endocrine therapy. [ESMO Congress 2024, abstract 1814O]

“Overall, very few breast cancer free interval (BCFI) events were observed in the trial?just nine events, including three recurrences,” said senior investigator Dr Fedro Peccatori, Director of the Fertility and Procreation Unit within the Division of Gynecologic Oncology at the European Institute of Oncology IRCCS in Milan, Italy.

BCFI did not significantly differ between the breastfeeding and the nonbreastfeeding group at 12 months (1.1 percent vs 1.9 percent) and at 24 months (3.6 percent vs 3.1 percent), indicating that breastfeeding had no substantial impact on BCFI (HR, 1.12, 95 percent CI, 0.28 ? 4.5). BCFI was defined as the months from first live birth to the first invasive local, regional, or distant breast cancer recurrence or contralateral disease.

The takeaway, according to Pecatori, is that breastfeeding is possible for the majority of breast cancer patients.

“These data underline the interest of young breast cancer survivors in breastfeeding and reinforce the notion that breastfeeding counselling should be incorporated into their individualized support,” he said. “It’s time to start thinking of breast cancer survivors as women with all the rights, needs, and possibilities of women that never had cancer.”

POSITIVE enrolled 518 patients who were ≤42 years of age, had HR+ stage I-III breast cancer, had undergone 18?30 months of endocrine therapy (ET), and desired to become pregnant. The study protocol specified that patients discontinue ET within 1 month before enrolment, with a 3-month washout period before attempting pregnancy. ET was interrupted for up to 2 years to allow for attempting pregnancy, conception (or failure to conceive), delivery, and breastfeeding (if desired and if feasible). The patients were strongly recommended to resume ET after 2 years to complete the planned 5 to 10 years of treatment.

Of the patients, 317 patients had a live birth for a total of 232 babies. A total of 196 patients (62 percent) opted to breastfeed, mostly from the contralateral breast, for a median duration of 4.4 months. Breastfeeding was more likely among patients older than 35 years (62.8 percent vs 51.2 percent), those with no prior children (85.4 percent vs 71.7 percent), and those who underwent breast-conserving surgery (66.3 percent vs 30.6 percent).

Duration of prior ET and time from enrolment to first live birth were not associated with breastfeeding frequency or duration.

Empowering patients and physicians

In a news release, study discussant Dr Maria-Alice Franzoi from Gustave Roussy in Villejuif, France, said: “The studies presented at the Congress significantly enhance the quality of available data and will be valuable in guiding patient-centred decision-making in clinical settings. We should empower both patients and providers with the feasibility and safety data from these studies to encourage early discussions in the care pathway.

“Ideally, women should receive counselling both before (starting at diagnosis) and after pregnancy. For young women with BRCA mutation-positive disease, the option of delaying prophylactic bilateral mastectomy for those who wish to become pregnant and breastfeed should be part of the shared decision-making process.”

Franzoi believed that breastfeeding can serve as a healing experience, helping restore a sense of normalcy and bodily function for women after breast cancer. This experience, she added, can facilitate reintegration into social and family life, in addition to strengthening the bond with the child, which should be properly evaluated in future prospective studies.