CD274 and triple-negative breast carcinoma: By contrast, triple-negative breast cancer (TNBC)—~10–15% of cases—lacks HER2 and hormone-receptor expression and remains clinically challenging with fewer validated targets; although recent advances such as pembrolizumab in PD-L1–positive disease and the TROP2-directed antibody–drug conjugate sacituzumab govitecan have improved outcomes, overall survival remains inferior to that seen in HER2-positive disease, underscoring an ongoing unmet need [90,91].