PDCD1 and breast carcinoma: Additionally, in a study involving 172 head and neck squamous cell carcinoma patients treated with Pembrolizumab (an anti-PD-1 monoclonal antibody), it was found that the overall response rate was twice as high in cancer patients positive for both ligands, compared with patients only PD-L1-positive [69], emphasizing that PD-L2 expression may also stratify cats with mammary carcinoma most likely to benefit from anti-PD-1 immunotherapy.