D2-40 Antibody is a Specific Marker for B2 Thymomas

The correlation between the worse outcome of thymomas and expression of podoplanin (D2-40 antibody) in neoplastic cells has been proved in recent studies. We investigated the expression of podoplanin in thymic epithelial tumors of different histologic types and stages resected in our institution. The presence and type of reaction (membranous or cytoplasmic) with D2-40 antibody were assessed. Analyzed group consisted of 72 tumors: 3 type A, 19 type AB, 5 type B1, 24 type B2, 4 type B3, 2 micronodular, 1 metaplastic, and 9 combined B2B3 thymomas and 5 thymic carcinomas. Positive reaction with D2-40 was detected in 7 cases (37%) of AB type, 2 (40%) of B1, 28 (85%) of B2, 3 (23%) of B3, and 1 case (100%) of metaplastic thymoma. All positive B2 and 2 cases of B3 thymomas revealed membranous type of reaction, whereas other subtypes showed less conspicuous cytoplasmic reactivity. A correlation between B2 thymoma and membranous type of reaction was statistically significant (P<0.0001). There was also a slight relationship between cytoplasmic type of reaction and AB or B1 thymomas (P=0.0256). No correlation was detected between D2-40-reactivity and stage (P=0.4) or myasthenic symptoms (P=0.21). In conclusion, membranous type of reaction with D2-40 antibody in thymomas is highly specific for B2 subtype, but antipodoplanin immunoreactivity has no relationship with the tumor stage.