1814O - Breastfeeding in women with hormone receptor-positive breast cancer who conceived after temporary interruption of endocrine therapy: Results from the POSITIVE trial

Background

The POSITIVE trial demonstrated no increase in short-term risk of breast cancer (BC) events in women with hormone receptor–positive (HR+) early BC who temporarily interrupted treatment to attempt pregnancy, after receiving 18 - 30 months of adjuvant endocrine therapy (ET). No prior prospective data detail breastfeeding patterns and behaviors in women with previous BC, and little is known about the impact of breastfeeding on BC outcomes.

Methods

Breastfeeding was a secondary endpoint of the POSITIVE trial. The evaluable dataset consisted of women who had at least one live birth on study. Here we describe breastfeeding frequency, duration, and laterality, and estimate the cumulative incidence of BC events by breastfeeding status. For this analysis, we recalculated breast cancer free interval (BCFI) from the date of first live birth to first invasive local, regional, or distant BC recurrence or contralateral BC.

Results

At a median follow-up of 41 months, 317 patients gave birth, of whom 196 (62%) breastfed, a total of 232 babies. Breastfeeding was from the contralateral breast in all but 2 patients while only 38 patients (12%) breastfed from both breasts. The frequency of breastfeeding was higher in women older than 35 years of age (62.8% vs. 51.2%), with no prior children (85.4% vs. 71.7%) and who underwent breast-conserving surgery (66.3% vs. 30.6%). 103/196 (52.6%) breastfed their first child for >4 months (median 4.4 months) (95% CI: 4.0 – 5.3). Duration of prior ET and time from enrollment to first live birth were not associated with breastfeeding frequency or duration. Breastfeeding did not impact the BCFI (HR: 1.12, 95% CI: 0.28 – 4.5) with few reported events (N=9), of which 3 were local recurrences. At 2 years from the first live birth, the cumulative incidence of BCFI was 3.6% and 3.1% in the breastfeeding and non-breastfeeding groups, respectively.

Conclusions

In POSITIVE, nearly two-thirds of women who gave birth breastfed, including >50% for more than 4 months. No impact on BC-related events was observed although longer follow-up is warranted. These results are key for women who wish to pursue pregnancy and breastfeeding after BC.

Clinical trial identification

NCT02308085.

Editorial acknowledgement

Legal entity responsible for the study

International Breast Cancer Study Group (IBCSG).

Funding

The POSITIVE trial was supported by the ETOP IBCSG Partners Q:10 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. Globally, the trial receives grant support for central or local trial conduct from the following: the International Breast Cancer Study Group (IBCSG); Frontier Science and Technology Research Foundation, Southern Europe (Frontier Southern Europe), Pink Ribbon Switzerland, Rising Tide Foundation for Clinical Cancer Research (CCR-15-120; CCR-20-200), Swiss Cancer League (KLS-3361-02), San Salvatore Foundation, Swiss Group for Clinical Cancer Research, Clinical Cancer Research Foundation of Eastern Switzerland, Ms Elisabetta Pavesi, Roche Diagnostics International, Verein Bärgüf, Swiss Cancer Foundation, Piajoh Fondazione di Famiglia, Gruppo Giovani Pazienti “Anna dai Capelli Corti,” and Schweizer Frauenlauf Bern—all in Switzerland; BIG Against Breast Cancer and the Baillet Latour Fund, Belgium; Gateway for Cancer Research (G-15-1900) and Breast Cancer Research Foundation—both in the United States; C & A, Germany; Dutch Cancer Society, the Netherlands; Norwegian Breast Cancer Society and Pink Ribbon—both in Norway; ELGC K.K. and Pink Ring—both in Japan; Mr Yong Seop Lee, Ms Sun Hee Kang, and Korean Breast Cancer Foundation—all in South Korea; and other private donors. In North America, the Alliance for Clinical Trials in Oncology receives support from the National Cancer Institute of the National Institutes of Health (NIH; Alliance for Clinical Trials in Oncology National Cancer Institute Community Oncology Research Program [NCORP] grant UG1CA189823) and the biorepository resource grant U24CA196171; the Eastern Cooperative Oncology Group–American College of Radiology Imaging Network (ECOG-ACRIN) receives support under grant UG1CA189828; SWOG Cancer Research Network receives support under NIH grants UG1CA189974 and U10CA180888; and NRG Oncology receives support under NIH grant U10CA180868 and NCORP grant UG1CA189867. Canadian Cancer Trials Group (CCTG) participation in the trial was supported through its grant from the National Cancer Institute of the NIH (CA180863). Funding support from the Dutch Cancer Society, the Netherlands (KaWeFis Batch7/7723). Additional programmatic funding support for the CCTG is provided by the Canadian Cancer Society (707213) and the Canada Foundation for Innovation. In addition, the trial receives support from RETHINK Breast Cancer, Canada, and the Gilson Family Foundation, United States.

Disclosure

H.A. Azim Jr: Financial Interests, Personal, Speaker, Consultant, Advisor: PEP therapy, Evexta Bio. A.H. Partridge: Financial Interests, Personal, Research Funding: Novartis. M.A. Colleoni: Financial Interests, Institutional, Research Grant: ROCHE; Non-Financial Interests, Leadership Role, Co-Chair Scientific Committee: International Breast Cancer Study Group. C. Saura Manich: Financial Interests, Personal, Speaker, Consultant, Advisor: AstraZeneca, Daiichi Sankyo, Pierre Fabre, Puma biotechnology; Financial Interests, Personal, Advisory Board: Eisai, Medtech, Roche, Novartis, Pfizer, Gilead, Pharmalex; Financial Interests, Personal, Speaker’s Bureau: Lilly, Seagen. C. Shimizu: Financial Interests, Personal, Funding: AstraZeneca, Chugai Pharma, Kyowa Kirin, Pfizer; Financial Interests, Personal, Research Funding: Lilly. J.R. Kroep: Financial Interests, Institutional, Advisory Board: AstraZeneca, Novartis, Lilly, GSK, Immagene; Financial Interests, Institutional, Research Funding: AstraZeneca, Novartis, Phillips research. K.A. Gelmon: Financial Interests, Personal, Advisory Board: AstraZeneca, Pfizer, Lilly, Novartis, Merck, Gilead, Seagen, City of Hope, Celcuity; Financial Interests, Institutional, Coordinating PI: AstraZeneca; Financial Interests, Institutional, Local PI: Pfizer, BMS. F. Amant: Financial Interests, Personal, Other, Honoraria: Roche; Financial Interests, Personal, Advisory Board: MiMark. A. Mailliez: Financial Interests, Personal, Speaker, Consultant, Advisor: Seagen; Financial Interests, Personal, Other, travel expenses: Lilly, Menarini, MSD Oncology, Novartis. H. Moore: Financial Interests, Personal, Advisory Board: Myovant Sciences; Financial Interests, Institutional, Research Funding: Daiichi Sankyo, Roche, AstraZeneca, Sermonix Pharma, Seagen. R.D. Gelber: Financial Interests, Institutional, Research Funding: AstraZeneca, Roche, Merck. O. Pagani: Financial Interests, Personal, Speaker, Consultant, Advisor: Roche, Debiopharm Group. All other authors have declared no conflicts of interest.