CD274 and thymoma: PD-L1 expression, while observed in more than 90% of epithelial cells of the normal thymus with a medullar tropism respecting Hassall's corpuscles [28], has also been identified in thymomas and thymic carcinomas using various immunohistochemistry protocols (Table 2) [[29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47]]; overall, expression of PD-L1 is common in thymomas and thymic carcinomas, and is usually high and intense.