High Expression of Programmed Death Ligand 1 and Programmed Death Ligand 2 in Ophthalmic Sebaceous Carcinoma: The Case for a Clinical Trial of Checkpoint Inhibitors.PURPOSE
 To evaluate the expression of programmed death ligand 1 (PD-L1) and programmed death ligand 2 (PD-L2) in ocular adnexal sebaceous carcinoma (OASC), and to appraise these findings within the context of recent comparable studies.


 Retrospective case series.


 Twenty cases of primary OASC were immunostained for PD-L1, PD-L2 and CD8.  PD-L1 and PD-L2 expression were graded with both the combined positive score (CPS) and the tumor proportion score (TPS).  Both raw CPS and TPS were reported, as well as positivity with TPS and CPS ≥1.  CD8 expression was graded on a 0-3 scale.  Charts were reviewed for clinical correlations.  The results of the current study were compared with results of similar recent investigations.


 For the 20 cases, mean expression of PD-L1 with CPS was 29.7 (range 0-101.5) and with TPS was 12.2 (range 0-95.8); mean expression of PD-L2 with CPS was 7.9 (range 0-37.3) and with TPS was 1.9 (range 0-12.9).  PD-L1 CPS ≥1 was detected in 95% of OASC, while PD-L1 TPS ≥1 was found in 75%.  PD-L2 CPS ≥1 was present in 60%, while only 20% had PD-L2 TPS ≥1.  Immune cells appeared to contribute to a substantial proportion of PD-L1 and PD-L2 positivity, and a conspicuous CD8-positive T-lymphocytic infiltrate was present in most tumors.  Significant correlations were identified between tissue expression of PD-L1, PD-L2, and CD8.  Tissues with greater levels of PD-L1 tended to express higher levels of PD-L2 and CD8.  The degree of PD-L1 and PD-L2 expression was also associated with the area in millimeters squared of the immunostained tumor, suggesting that tumor sampling may influence interpretation of PD-L1 and PD-L2 expression in ocular adnexal tumors.


 CONCLUSIONS
 The current and preceding studies confirm that PD-L1 and PD-L2 are expressed in a high percentage of OASCs.  These results support the premise that checkpoint inhibitor drugs hold considerable therapeutic promise for patients with OASC and stimulate the institution of clinical trials.
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