Beyond a single disease: review of rare histological subtypes of triple-negative breast cancer with implications for prognosis and treatment

Triple-negative breast cancer (TNBC) is commonly approached as a single clinical entity despite marked biological heterogeneity. A subset of cases corresponds to rare histologic subtypes that display distinct molecular drivers, immune microenvironments, and clinical behavior. In this Review, we summarize the clinicopathologic and molecular features of rare TNBC histologies and discuss emerging therapeutic vulnerabilities. Integrating histologic classification with molecular profiling may enable more precise risk stratification and guide biomarker-driven treatment strategies.