Background & objective: The World Health Organization (WHO) histological classification of thymoma was published in 1999. This study was to investigate the correlations of WHO histological classification of thymoma to its clinical characteristics and prognosis.
Methods: Records of 82 thymoma patients treated with surgery were reviewed retrospectively. Histological diagnosis based on WHO classification system was made by an experienced pathologist. The correlations of WHO histological classification of thymoma to its clinical characteristics and prognosis were analyzed.
Results: Of the 82 cases, 5 (6.1%) were type A, 21 (25.6%) were type AB, 14 (17.1%) were type B1, 12 (14.6%) were type B2, 14 (17.1%) were type B3, and 16 (19.5%) were type C; according to Masaoka clinical staging system, 29 (35.4%) were in stage I, 13 (15.8%) in stage II , 32 (39%) in stage III , and 8 (9.8%) in stage IVa. The histological subtype of thymoma was significantly correlated with clinical stage (chi2 = 47.29, P < 0.001) and tumor invasive degree (chi2 = 30.78, P < 0.001). Complete resection rate was significantly higher in patients with type A, AB, B1 or B2 tumors than in patients with type B3 or C tumors (84.6% vs. 50.0%, chi2 = 11.29, P = 0.002). The 5-year survival rates of patients with stage I, II, III , and IVa were 100%, 100%, 69.5%, and 37.5%, respectively; the 10-57.1%, year survival rates were 88.1%, 47.5, and 0, respectively. The difference of survival rates among different clinical stages (log-rank = 40.31, P < 0.001) and histological subtypes (log-rank = 16.0, P = 0.007) were significant.
Conclusion: To some extent, the WHO histological classification reflects the biological behavior and clinical characteristics of thymoma, and may be helpful in diagnosing and treating thymoma.