Background: In a number of human malignancies, tumor-associated macrophages (TAMs) are closely involved in tumor progression. On the other hand, dendritic cells (DCs) that infiltrate tumor tissues are involved in tumor suppression. However, there have been very few reports on the distribution profiles of TAMs and DCs in thymic epithelial tumors. We examined the difference in the distribution profiles between TAMs and DCs in thymoma and thymic carcinoma.
Methods: We examined 69 samples of surgically resected thymic epithelial tumors, namely, 16 thymic carcinomas and 53 thymomas, in which we immunohistochemically evaluated the presence of TAMs using CD68 and CD163 as markers and DCs using S100 as the marker in tumor tissue samples in comparison with normal thymic tissues.
Results: The percentage of samples with a large number of CD68+ TAMs was not significantly different between thymic carcinoma and thymoma (7/16 versus 16/53, p = 0.904). However, the percentage of sample with a large number of CD163+ TAMs was significantly higher in thymic carcinoma than in thymoma (15/16 versus 34/53, p = 0.024). In contrast, the percentage of samples with a large number of S100+ DCs was significantly lower in thymic carcinoma than in thymoma (2/16 versus 23/53, p = 0.021).
Conclusions: To the best of our knowledge, we are the first to show a high percentage of CD163+ TAMs and a low percentage of S100+ DCs in thymic carcinoma samples, and our findings may provide an idea for future targeted therapeutic strategies for thymic carcinoma using antibodies that inhibit monocyte differentiation to TAMs, thereby skewing TAMs differentiation toward DCs.