title: Immunohistochemical status of PD-L1 in thymoma and thymic carcinoma.
abstract: OBJECTIVE
  The immune checkpoint ligand programmed cell death 1 ligand 1 (PD-L1) is expressed in various tumors and is associated with the response to anti programmed cell death 1 (PD-1)/PD-L1 drugs. We evaluated PD-L1 expression in thymomas and thymic carcinomas to determine whether PD-L1 represents a therapeutic target in unresectable thymomas or thymic carcinomas that could be amenable to antibody-based immunotherapy.
  
  
  METHODS
  A tissue microarray (TMA) comprised of 101 thymomas and 38 thymic carcinomas samples was evaluated. After validation of the rabbit monoclonal PD-L1 antibody (clone E1L3N), the TMA was stained and the tumor PD-L1 expression score was calculated using a semiquantitive method (by multiplying the intensity [0-3] by the staining area [0-100%]).
  
  
  RESULTS
  Seventy percent of thymic carcinoma (type C) and 23% of thymoma (types A, AB, and B) samples stained positive for PD-L1 (P<.001). A WHO classification (type C vs types A, AB, and B) was significantly associated with positive PD-L1 expression (P=0.006), though multivariate analysis did not show PD-L1 positive was a significant negative factor of overall survival (hazard ratio=0.99, 95% confidence interval=0.35-2.73; P=0.987).
  
  
  CONCLUSIONS
  To the best of our knowledge, this is the largest-scale study to evaluate PD-L1 expression in thymomas and thymic carcinomas. The data suggest that the anti PD-1/PD-L1 drug could be of potential use in immunotherapy for unresectable or relapsed thymomas and thymic carcinomas.
authors: Division of Pathology and Clinical Laboratory, National Cancer Center Hospital, Tokyo, Japan; Department of Thoracic Oncology, National Cancer Center Hospital, Tokyo, Japan.
authors: Yuki
authors: Y
authors: Katsuya
authors: Division of Molecular and Cellular Medicine, National Cancer Center Research Institute, Tokyo, Japan.
authors: Yu
authors: Y
authors: Fujita
authors: Department of Thoracic Oncology, National Cancer Center Hospital, Tokyo, Japan.
authors: Hidehito
authors: H
authors: Horinouchi
authors: Department of Thoracic Oncology, National Cancer Center Hospital, Tokyo, Japan.
authors: Yuichiro
authors: Y
authors: Ohe
authors: Division of Thoracic Surgery, National Cancer Center Hospital, Tokyo, Japan.
authors: Shun-Ichi
authors: S
authors: Watanabe
authors: Division of Pathology and Clinical Laboratory, National Cancer Center Hospital, Tokyo, Japan. Electronic address: ktsuta@ncc.go.jp.
authors: Koji
authors: K
authors: Tsuta
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000911:Antibodies, Monoclonal / Q000378:metabolism; D060890:B7-H1 Antigen / Q000378:metabolism*; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D008297:Male; D008875:Middle Aged; D061026:Programmed Cell Death 1 Receptor / Q000378:metabolism; D013945:Thymoma / Q000378:metabolism* / Q000473:pathology*; D013953:Thymus Neoplasms / Q000378:metabolism* / Q000473:pathology*
chemical_list: D000911:Antibodies, Monoclonal; D060890:B7-H1 Antigen; C423236:CD274 protein, human; C105992:PDCD1 protein, human; D061026:Programmed Cell Death 1 Receptor
keywords: Clone E1L3N; Immunohistochemistry; PD-1; PD-L1; Thymic carcinoma; Thymoma