Postpartum Breast Cancer: Distinct Clinical Features and the Role of Abrupt Breastfeeding Cessation

Background: Postpartum breast cancer (PPBC), diagnosed within 10 years after delivery, exhibits distinct biological-clinical characteristics and is associated with poorer prognosis. This study aimed to explore factors linked to PPBC and identify possible differential prognostic markers. Methods: We conducted a retrospective case-control study including women under 45 years. Clinical-reproductive and histopathological data, including previous gynecological pathology and benign breast conditions, were collected through standardized questionnaires and verified with medical records when available. PPBC was compared with non-postpartum breast cancer (non-PPBC) and healthy women. Multivariate analysis identified independent risk factors. Results: Among 2,698 women, 264 (9.8%) had breast cancer, including 134 PPBC and 130 non-PPBC, whereas 2,434 served as healthy controls. Previous gynecological pathology was more frequent among PPBC than healthy mothers (48.9% vs. 25.7%; p < 0.001). Same occurred with previous breast pathology (51.9% vs. 21.7%; p < 0.001). The percentage of women who abruptly discontinued breastfeeding was higher in PPBC (27.5%) compared with healthy mothers (12.6%; p < 0.001). PPBC was more diagnosed at stage II (63.9%); non-PPBC at stage I (64.9%) ( p = 0.002). Early-PPBC (<5 years postpartum) showed higher Ki67-expression ( p = 0.012) and lower estrogen-receptor positivity ( p = 0.002). Previous breast pathology (odds ratio [OR] = 2.2; 95% confidence interval [CI]: 1.45–3.34; p < 0.001) and abrupt cessation of breastfeeding (OR = 2.6; 95% CI: 1.63–4.08; p < 0.001) were the only factors independently associated with the risk of developing PPBC. Conclusions: PPBC presents distinct features and represents specific tumor entity. Abrupt cessation of breastfeeding appears to be a potentially modifiable risk factor.