Timing of breast cancer diagnosis postpartum and survival in women with germline pathogenic variants.

Prognostic modification linked to time since last childbirth and to breastfeeding in women carrying pathogenic variants in breast cancer susceptibility genes.

Parity and breastfeeding reduce lifetime breast cancer risk, but the postpartum period is associated with transiently increased risk and poor outcomes. This Australian retrospective cohort included 1,200 women carrying class 4 or 5 pathogenic variants in high- or moderate-penetrance breast cancer susceptibility genes, with invasive breast cancer and no pregnancy after diagnosis, enrolled in the Kathleen Cuningham Foundation Consortium from 1980 to 2022 (median follow-up 13 years). Diagnosis 10 or more years postpartum applied to 52% of women, versus 32% under 10 years and 16% nulliparous; women diagnosed less than 10 years postpartum were younger (36 versus 48 years, P < 0.001), more likely to carry BRCA1 variants and more likely to have oestrogen receptor-negative disease. Diagnosis 10 or more years postpartum was associated with better overall survival than nulliparity (hazard ratio 0.63; 95% CI 0.43-0.92; P = 0.02). In parous women, breastfeeding (HR 0.49; 0.33-0.73; P < 0.001) and an interval of 10 or more years since last childbirth (HR 0.48; 0.31-0.74; P < 0.001) independently predicted better overall survival.

Synthesis written by Geno'X. For the full original abstract, please refer to the source publication.

Both associations are strong but highly exposed to confounding: women diagnosed within ten years postpartum are twelve years younger, more often BRCA1 carriers and more often oestrogen receptor-negative, three features that carry part of the prognosis on their own despite adjustment. The hazard ratio of 0.49 for breastfeeding is the most intriguing and the most fragile result: advising a BRCA1 carrier to breastfeed is not a neutral recommendation, and a retrospective association is not enough to ground it. To be used as a prognostic element for discussion, not as reproductive advice.

Analysis by Dr Thibaut Benquey