Objective  To explore the expression of PD-L1 and p53 in recurrent thymoma and its relationship to the World Health Organization (WHO) classification of thymoma.

  Methods  We reviewed the histopathological records of patients with a complete thymoma resection between January 2008 and December 2015 at the Second Affiliated Hospital of Zhejiang University School of Medicine. Immunohistochemical staining for PD-L1 and p53 markers was performed on specimens from patients with valid telephone follow-up. WHO classifications and immunohistochemical expression of PD-L1 and p53 in the recurrent and non-recurrent groups were statistically analyzed.

  Results  Twenty patients of recurrent thymoma (13 males and 7 females) and 61 patients of non-recurrent thymoma (27 males and 34 females) were enrolled. There was a statistically significant difference in the WHO classifications and variants between the recurrent and the non-recurrent groups (P=0.001). The total recurrence rate in 81 cases was 24.7%. Among the WHO classifications, the recurrence rate of type A was the lowest (0%), and the recurrence rate of type C was the highest (57.1%). The differences in the recurrence rate among WHO subtypes were statistically significant (P=0.017). The PD-L1 and p53 expression scores were statistically significantly higher in the recurrent group than those in the non-recurrent group (P=0.02 and 0.019, respectively). In all specimens, there was a significant positive correlation between the PD-L1 expression score and WHO classification (R=0.358, P=0.001); the PD-L1 expression score was shown to significantly positively correlate with p53 expression grade (R=0.317, P=0.004).

  Conclusions  WHO classification as well as PD-L1 and p53 expression in thymoma could play important roles in predicting harmful recurrent behavior.