title: Clinicopathologic and Prognostic Implications of Programmed Death Ligand 1 Expression in Thymoma.
abstract: BACKGROUND
  Programmed death ligand 1 (PD-L1) has been reported to be expressed in various malignancies and is considered to be a prognostic factor and an immunotherapeutic target. The aim of this study was to characterize PD-L1 expression in thymoma and determine statistical associations between this expression and clinical features.
  
  
  METHODS
  We reviewed formalin-fixed, paraffin-embedded tissue specimens from 82 thymoma cases accumulated at Kurume University, the majority of which achieved surgical complete resection. Expression of PD-L1 was evaluated by immunohistochemistry. Statistical associations between PD-L1 expression and clinicopathologic features were evaluated by using χ(2) test and Fisher's exact test. Disease-free survival and overall survival curves were established by the Kaplan-Meier method and compared using a log-rank test. Predictive factors for disease-free survival after complete resection were analyzed by using a Cox proportional hazards model in univariate and multivariate analysis.
  
  
  RESULTS
  Overall, 44 thymoma cases (54%) revealed high PD-L1 expression. High PD-L1 expression was statistically associated with Masaoka stage III/IV disease (p = 0.043) and World Health Organization type B2 or B3 thymoma (p = 0.044). Disease-free survival after complete resection in high PD-L1 expression was significantly worse than that in low PD-L1 expression (p = 0.021), although there was no significant difference in overall survival (p = 0.957). Multivariate analysis also revealed high PD-L1 expression as an independent risk factor for recurrence (p = 0.008).
  
  
  CONCLUSIONS
  Characterization of PD-L1 expression in thymoma should enable more effective clinical approaches, including prognostic stratification of patients and potential use of anti-PD-L1 antibody immunotherapy.
authors.affiliation: Department of Surgery, Kurume University School of Medicine, Kurume, Japan.
authors.forename: Shintaro
authors.initials: S
authors.lastname: Yokoyama
authors.affiliation: Department of Pathology, Kurume University School of Medicine, Kurume, Japan. Electronic address: miyoshi_hiroaki@med.kurume-u.ac.jp.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Miyoshi
authors.affiliation: Department of Surgery, Kurume University School of Medicine, Kurume, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Nishi
authors.affiliation: Department of Surgery, Kurume University School of Medicine, Kurume, Japan.
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Hashiguchi
authors.affiliation: Department of Surgery, Kurume University School of Medicine, Kurume, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Mitsuoka
authors.affiliation: Department of Surgery, Kurume University School of Medicine, Kurume, Japan.
authors.forename: Shinzo
authors.initials: S
authors.lastname: Takamori
authors.affiliation: Department of Surgery, Kurume University School of Medicine, Kurume, Japan.
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Akagi
authors.affiliation: Biostatistics Center, Kurume University, Kurume, Japan.
authors.forename: Tatsuyuki
authors.initials: T
authors.lastname: Kakuma
authors.affiliation: Department of Pathology, Kurume University School of Medicine, Kurume, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Ohshima
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000951:Antigens, Neoplasm / Q000378:metabolism*; D060890:B7-H1 Antigen / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D011237:Predictive Value of Tests; D011379:Prognosis; D012372:ROC Curve; D012189:Retrospective Studies; D013945:Thymoma / Q000378:metabolism* / Q000473:pathology* / Q000601:surgery; D013953:Thymus Neoplasms / Q000378:metabolism* / Q000473:pathology* / Q000601:surgery
chemical_list: D000951:Antigens, Neoplasm; D060890:B7-H1 Antigen