Comparative analysis of the tumor immune microenvironment between thymoma and thymic carcinoma

Thymic epithelial tumors (TETs) often linked with autoimmune syndromes such as myasthenia gravis (MG), have an underexplored tumor immune microenvironment (TIME), limiting the effective use of Immune Checkpoint Inhibitors. This study aims to address the immunology of TETs, focusing on the prognostic significance of TIME and its association with MG. This study investigates the TIME in TET subtypes, thymic carcinoma (TC) and thymoma, assesses their prognoses, and examines the relationship between thymoma's immune microenvironment and MG.

This study included 157 patients with TET who underwent surgical resection at Juntendo Hospital between January 2012 and September 2020. Immune cell densities of tissue specimens were analyzed using multiplex fluorescence immunohistochemical staining.

Thymoma and TC were diagnosed in 145 and 12 patients, respectively. Thymoma types B1 and B2 showed elevated CD4⁺ and CD8⁺ T cells, while TC had decreased T cells and increased Foxp3⁺ T cells. Thymoma with MG had higher CD20⁺CD79a^- cells counts in the stromal area compared to those without MG (p = 0.0165). Elevated CD4⁺ T cells (p = 0.0310), CD8⁺ T cells (p = 0.0215), and CD68⁺ cells (p = 0.0432) in the tumor area were linked to good prognosis, while higher CD20⁺CD79a^- cells in the stromal area indicated poor prognosis (p = 0.0088).

Thymomas had a higher prevalence of T cells compared to TC. CD4⁺ T cells, CD8⁺ T cells, and CD68⁺ cells in the tumor area were favorable prognostic markers, while B cells in the stromal area indicated a poor prognosis for thymoma.