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Background The testis is an immune-privileged organ due to its lack of functional HLA class I expression. However, the expression status of HLA class I in testicular seminoma—characterized histologically by lymphocytic infiltration—remains unclear.Methods We performed immunohistochemistry to evaluate HLA class I expression and its spatial relationship with CD8-positive cells in 20 cases of stage I seminoma. Each specimen was scored manually and further analyzed using the HALO image analysis platform (Indica Labs, New Mexico, USA).Results Manual scoring and HALO analysis showed 80% concordance. HLA class I expression was positive in 13 cases (65%). Based on HLA class I expression levels, tumors were classified into three categories ( figure 1). The number of infiltrating CD8-positive cells significantly correlated with HLA class I expression. Spatial analysis revealed that tumors with higher HLA class I expression had shorter distances between HLA class I-positive tumor cells and CD8-positive cells (figure 2).Conclusions Seminoma cells expressing HLA class I were frequently located in close proximity to CD8-positive T cells, suggesting a spatial relationship that may influence the tumor immune microenvironment.Abstract 1114 Figure 1Representative immunohistochemistry images illustrating three categories of HLA class I expression in seminoma specimens: negative, low, and high. Color coding: Red, HLA class I-positive tumor; Blue, HLA class I-negative tumor; Yellow, CD8+ T cellAbstract 1114 Figure 2(A) In regions where tumor cells expressed higher levels of HLA class I, the proportion of CD8+ T cells were significantly increased. (B) Spatial analysis revealed a proportional decrease in the distance between HLA class I-positive tumor and CD8+ T cell