Expression of podoplanin in thymoma: its correlation with tumor invasion, nodal metastasis, and poor clinical outcome.

Recent studies have shown that podoplanin overexpression is associated with lymph node metastasis and poor clinical outcome in several malignant tumors. To investigate the role of podoplanin in thymoma, we examined 111 thymomas by immunohistochemistry using monoclonal antibody D2-40, which recognizes podoplanin. The tumors consisted of 8 type A, 40 type AB, 15 type B1, 23 type B2, 15 type B3, and 10 combined thymomas according to the World Health Organization histological classification system and of 41 stage I, 28 stage II, 16 stage III, 20 stage IVa, and 6 stage IVb thymomas according to the Masaoka staging system. We have found podoplanin expression in 0 (0%) type A, 4 (10%) type AB, 4 (27%) type B1, 16 (70%) type B2, 10 (67%) type B3, and 7 (70%) combined thymomas and in 5 (12%) cases of stage I, 7 (25%) of stage II, 11 (69%) of stage III, 12 (60%) of stage IVa, and all (100%) of stage IVb thymomas. Podoplanin was significantly expressed in B2/B3/combined thymomas and advanced stage thymomas (P < .0001). On survival analysis, podoplanin expression was significantly associated with an increased risk of death for the whole group of thymomas (P = .0002), although it was not identified as an independent prognostic factor in multivariate analysis. The significant survival curve differences of podoplanin expression were also seen for stage III/IVa/IVb thymomas (P = .0409) and B2/B3/combined thymomas (P = .0478). In conclusion, D2-40 immunostaining seems to be valuable for predicting the aggressive and metastatic potential of thymomas and the prognosis of the patients.