CD274 and squamous cell carcinoma: Subsequently, using clinical materials from dogs with tumors, we investigated the expression of PD-L1 by flow cytometry and identified PD-L1 expression on cells from angiosarcoma, hepatocellular carcinoma, squamous carcinoma, and breast adenocarcinoma; PD-L1 was not detectable on the lymphocytes from control dogs (Fig. 5B, Table 4).