PD‐1 and PD‐L1 expression in Kaposi sarcoma: A comparative study according to the pathological stage and clinical characteristics

Background Kaposi sarcoma (KS) is a mesenchymal tumor with distinct histopathological features according to stage of progression. Programmed death‐1 (PD‐1) and its ligand PD‐L1 play major roles in the immune escape strategy of tumors. Objectives This study evaluated expression of PD‐1 and PD‐L1 in various stages of KS and investigated associations between their expression and clinical characteristics. Methods Fifty cases with histopathologically diagnosed KS were classified as early or late stage. These specimens were stained with anti‐PD‐1 and anti‐PD‐L1 antibodies. The extent of expression in the intratumoral and peritumoral areas was judged by two dermatopathologists. Results PD‐1 and PD‐L1 were expressed in 72.2% (13/18) and 11.1% (2/18) of early‐stage cases, respectively, compared with 43.8% (14/32) and 28.1% (9/32) of late‐stage cases, respectively. At the late stage, PD‐1 expression was significantly higher in the peritumoral area than in the intratumoral area (P = 0.001). PD‐1 expression in the intratumoral area was significantly higher at the early stage than at the late stage (P = 0.013). PD‐L1 expression in the peritumoral area was significantly higher at the late stage than at the early stage (P = 0.038). Conclusions The pattern of PD‐1 and PD‐L1 expression differs according to the stage of KS, but is unaffected by clinical variables.