PD-L1 expression in HER2+ breast cancer, on the other hand, has some caveats that support its use it as a biomarker of the success of anti-PD-1/PD-L1 antibody treatment in combination with HER2-targeted therapies, as stated in the section on PD-1 and PD-L1 antibodies, and more studies in that direction are granted. The gene discussed is ERBB2; the disease is breast cancer.