HOXD13 and nonpapillary renal cell carcinoma: sPD-1 levels demonstrated a strong relationship with tumor histological type, with patients diagnosed with non-clear cell RCC (nccRCC) showing markedly higher median levels (87.01 pg/mL; IQR: 74.39–123.2) compared to those with clear cell RCC (ccRCC) (55.37 pg/mL; IQR: 40.62–72.64; p < 0.0001).