Prognostic value and immunological role of cathepsin S gene in pan‑cancer

. The cathepsin S (CTSS) gene encodes a lysine cysteine protease and serves an important role in the development of autoimmune diseases, inflammation and nervous system diseases. Furthermore, CTSS is implicated in tumor invasion and metastasis by the induction of tumor angiogenesis and the degradation of the tumor extracel‑ lular matrix. Nevertheless, the precise impact of CTSS on predicting pan‑cancer prognosis and its influence on the tumor microenvironment and immune infiltration in human cancers remains unknown. This present study employed a comprehensive array of bioinformatic methods to evaluate the expression of CTSS and its associations with prognosis, clinicopathological characteristics, tumor microenviron‑ ment, tumor immune infiltration, tumor mutational burden and microsatellite instability across numerous cancer types. The current study demonstrated abnormal expression and distinct genomic alteration profiles of CTSS in many of the cancers tested. Furthermore, CTSS expression exhibited close associations with the prognosis of numerous cancers. High CTSS expression was significantly associated with better overall survival and disease‑specific survival in bladder urothelial carcinoma (BLCA) and skin cutaneous melanoma (SKCM) but worse outcomes in brain lower grade glioma (LGG) and uveal melanoma (UVM). Moreover, CTSS demonstrated significant correlations with tumor mutational burden and microsatellite instability in 8 and 12 cancer types respectively, as well as different responses in immu‑ notherapy sub‑cohorts, especially in melanoma and bladder cancers. CTSS expression showed a positive correlation with stromal and immune cell scores in the four aforementioned cancers. Moreover, CTSS expression was correlated with the number of infiltrating CD8 + T cells, CD4 + T cells and macrophages. Conversely, CTSS was negatively associated with resting Mast cells, resting NK cells and resting memory CD4 + T cell infiltration in BLCA, SKCM and kidney renal clear cell carcinoma (KIRC). Furthermore, CTSS expression was correlated with immune‑related gene expression, notably PDCD1,