Clinicopathologic and Prognostic Implications of Programmed Death Ligand 1 Expression in Thymoma

Ann Thorac Surg. 2016 Apr;101(4):1361-9. doi: 10.1016/j.athoracsur.2015.10.044. Epub 2016 Jan 12.


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.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Antigens, Neoplasm / metabolism*
  • B7-H1 Antigen / metabolism*
  • Female
  • Humans
  • Male
  • Middle Aged
  • Neoplasm Staging
  • Predictive Value of Tests
  • Prognosis
  • ROC Curve
  • Retrospective Studies
  • Thymoma / metabolism*
  • Thymoma / pathology*
  • Thymoma / surgery
  • Thymus Neoplasms / metabolism*
  • Thymus Neoplasms / pathology*
  • Thymus Neoplasms / surgery


  • Antigens, Neoplasm
  • B7-H1 Antigen