Abstract
BACKGROUND: Thymic epithelial tumors (TETs) currently lack effective prognostic factors and novel treatment approaches, the aim of the study is to investigate the expression of CD55 in TETs and the relationship with clinicopathological characteristics and prognosis. METHODS: Firstly, 250 TETs, including 206 thymoma and 44 thymic squamous cell carcinomas (TSCC), were retrospectively selected. Subsequently, the expression levels of CD55 protein and mRNA were assessed using immunohistochemistry (IHC) and qRT-PCR. Finally, the relationship among CD55, clinicopathological characteristics, and prognosis was analyzed. RESULTS: The expression of CD55 mRNA and protein were higher in thymoma (p = 0.0148; p < 0.0001) and TSCC (both p < 0.0001) compared with normal thymus tissues. Immunohistochemically, the positive rate of CD55 was 80% (200/250) in TETs, mainly located in cytomembrane. 224 patients were successfully followed up, of which 33 patients developed progression. Univariate Cox regression analysis revealed that histological type, Masaoka-Koga stage, tumor completeness of resection, adjuvant therapy, CD55 mRNA, and protein (all p < 0.01) were significant factors affecting progression free survival (PFS). Multivariate Cox regression analysis showed that CD55 mRNA (p < 0.001), CD55 protein (p = 0.029), tumor completeness of resection (p = 0.010), and Masaoka-Koga stage (p = 0.006) were independent risk factors of PFS. In addition, Pearson's correlation analysis indicated a significant correlation between CD55 mRNA and protein, histological type, tumor completeness of resection, adjuvant therapy, and Masaoka-Koga stage (all p < 0.001). Unpaired T-test showed that the high expression of CD55 mRNA and protein were significantly associated with incomplete resection, higher histological grade, Masaoka-Koga stage, and adjuvant therapy (all p < 0.01). Furthermore, multivariate Cox analysis showed that CD55 mRNA (p < 0.001), CD55 protein (p = 0.037), tumor completeness of resection (p < 0.05) were independent risk factors of PFS in the high-risk TETs subgroup. CONCLUSIONS: The high expression of CD55 was related to poor prognosis of TETs. Moreover, its significant association with worse outcomes in high-risk TETs subgroup further underscores it its potential as a prognostic marker and therapeutic target, especially in TSCC.