Postpartum Breast Cancer in Young Women: A Biologically and Clinically Distinct Disease Entity

Postpartum breast cancer (PPBC), defined as breast cancer diagnosed within 5–10 years after childbirth, represents a unique and aggressive subtype of breast cancer in young women. Accounting for 35%–55% of breast cancer cases in women under 45 years, PPBC is characterized by distinct molecular features, heightened metastatic potential, and significantly worse prognosis compared to breast cancer in nulliparous women or older parous women. The postpartum mammary gland involution process creates a protumorigenic microenvironment through extensive tissue remodeling, immune modulation, and extracellular matrix changes that promote cancer progression. The liver also undergoes similar involution, potentially explaining the threefold increase in liver metastases observed in PPBC patients. Notably, women diagnosed with PPBC demonstrate significantly worse outcomes compared to nulliparous counterparts with current standard treatments, which show reduced efficacy in this population. This review comprehensively examines the pathophysiology and positions PPBC as a biologically distinct disease entity requiring specialized clinical management. Furthermore, we discuss promising therapeutic strategies targeting the unique biology of PPBC, including immunotherapy approaches, COX-2 inhibition, and microenvironment modulation. The review identifies critical knowledge gaps in PPBC research and proposes future directions to improve outcomes for this vulnerable patient population.