PD-1/PD-L1 expression is most commonly observed in triple-negative breast cancer (TNBC), followed by HER2+ BC, where PD-L1 expression of up to 58%, 53.8%, and 32% has been detected in tumor cells, immune cells, and both cells, respectively [200,201,202]. The gene discussed is ERBB2; the disease is triple-negative breast carcinoma.