Pregnancy-associated breast cancer at term: Vitamin D deficiency and a missed diagnostic window in pregnancy-associated malignancy

Pregnancy-associated breast cancer (PABC), defined as breast cancer diagnosed during pregnancy or within one year postpartum or any time during lactation, represents a distinct clinical challenge due to physiological breast changes that may obscure malignant findings and contribute to diagnostic delay. While increasing attention has been paid to breast cancer diagnosed during early and mid-pregnancy, malignancy presenting at term or in the immediate peripartum period remains comparatively under-explored. This Perspective uses a real-world clinical case diagnosed at term as a conceptual framework to highlight the peripartum period as a critical but often overlooked diagnostic window in pregnancy-associated malignancy. The case illustrates how persistent breast symptoms in late pregnancy may be misattributed to physiological changes, leading to delayed imaging and diagnosis despite frequent healthcare contact. In addition, the concurrent finding of severe maternal vitamin D deficiency (VDD) raises biologically plausible questions regarding its potential role in tumor behavior within the unique hormonal and immunological milieu of pregnancy. Beyond the individual clinical scenario, this article discusses broader implications for obstetric and oncologic practice, emphasizing the importance of maintaining a high index of suspicion for unilateral or progressive breast findings regardless of gestational age. The safety and accessibility of breast ultrasound during pregnancy support its use as a first-line diagnostic tool, including in late gestation. Multidisciplinary collaboration is essential to ensure timely diagnosis and to balance maternal oncologic management with fetal and neonatal safety. By drawing attention to diagnostic vulnerability at the time of delivery, this Perspective aims to promote earlier recognition of pregnancy-associated breast cancer and to encourage further research into modifiable biological factors, such as vitamin D status, that may influence disease presentation and outcomes.