Maternal and Neonatal Complications Associated with Breast Cancer Systemic Treatments — A VigiBase Disproportionality Analysis Study

Pregnancy‐associated breast cancer (PrBC) presents therapeutic challenges. Understanding maternal–fetal safety of systemic anticancer therapies is critical. We performed a case/non‐case disproportionality analysis using the WHO global pharmacovigilance database up to January 2024, to evaluate maternal–fetal outcomes associated with breast cancer (BC) systemic treatments. The exposure group consisted of reports mentioning a BC treatment at any time during pregnancy. The primary outcome was the reporting odds ratio (ROR) of maternal–fetal complications with the two cornerstone cytotoxic classes, anthracyclines (doxorubicin, epirubicin) and taxanes (docetaxel, paclitaxel), assessed individually vs. other anticancer treatments. Secondary analyses assessed all BC treatments and trimester‐specific risks. Of 3310 pregnancy‐related reports, 1789 involved BC treatments. Median maternal age was 27.4 years (SD 13.8) vs. 29.3 (SD 11.7) in the comparator group. Adverse maternal–fetal outcomes were reported in 998 (55.8%) BC treatment reports vs. 470 (30.9%) in other anticancer treatments. Anthracyclines were associated with neonatal hematologic disorders (ROR = 1.7, 95% CI = 1.1–2.5) and intrauterine growth restriction (IUGR) (ROR = 2.1, 95% CI = 1.7–2.7). Paclitaxel was linked to sensory defects including congenital ear/ocular anomalies (ROR = 5.2, 95% CI = 2.2–12.3); all 8 cases involved platinum co‐exposure (cisplatin: n = 5; carboplatin: n = 3), suggesting a platinum‐mediated mechanism; and to hyperbilirubinemia (ROR = 4.1, 95% CI = 2.0–8.4), and docetaxel to neonatal neurologic disorders (ROR = 3.6, 95% CI = 1.4–9.3). First‐trimester exposure ( n = 26) showed preliminary signals of increased congenital malformation risk, including face (ROR = 13, 95% CI = 2–79), and musculoskeletal malformation (ROR = 8, 95% CI = 1.1–60). This pharmacovigilance study identifies signals of disproportionate reporting of specific maternal and neonatal outcomes with BC treatments; these findings are hypothesis‐generating and require confirmation in prospective registries.