PDCD1 and cancer: Although discussion continues as to whether measuring PD-L1 expression in cancers is a clinically useful predictive biomarker for response to PD-1/PD-L1 inhibitors33, other PD-L1-positive cancers in dogs including osteosarcoma, hemangiosarcoma, mast cell tumour, mammary adenocarcinoma, lymphoma and prostate adenocarcinoma13, 15, 29, 31, could also be targeted by c4G12.