TROP2 expression in thymic carcinoma: Brief report

Introduction Trophoblast cell surface antigen 2 (TROP2) is a transmembrane glycoprotein overexpressed in various cancer types. Although TROP2-targeting therapy is currently attracting attention, little is known about TROP2 expression in thymic carcinoma. Methods TROP2 gene expression in thymic epithelial tumors was analyzed using RNA-seq data for 122 cases obtained from The Cancer Genome Atlas (TCGA). Immunohistochemistry (IHC) staining with anti-TROP2 antibody (SP295) was performed on 26 cases of thymic carcinoma tissues surgically resected at Juntendo University. Results RNA-seq data analysis from TCGA revealed that TACSTD2 (gene encoding TROP2) expression was significantly higher in thymic carcinoma compared to thymoma (padj = 6.64e-05). There was also a trend of increasing expression in the order of thymoma type B1, B2, B3, and thymic carcinoma. As for IHC in thymic carcinoma, TROP2 expression was localized to the membrane of cancer cells. Intensity 0/1/2 was observed in 6 (23.1%), 11 (42.3%), and 9 (34.6%) cases, respectively, leading to TROP2 positivity in 20 cases (76.9%). The median proportion of TROP2-positive tumor cells and the median H-score were 25.0% (range 0–100%) and 25.0 (range 0–200), respectively. No significant factors were identified in the analysis of TROP2 expression and patient background. Although not significant, high TROP2 expression (H-score ≥50) tended to be associated with shorter survival. Conclusions TROP2 expression in thymic carcinoma was confirmed by both RNA-seq and IHC, with high expression observed in IHC for intensity (76.9%) and proportion. TROP2 could be a potential target in thymic carcinoma.