CST4 and neoplasm: The cystatin family of genes encodes proteins known as cysteine protease inhibitors, which play vital parts in modulating protein turnover and maintaining cellular homeostasis.12 These genes have been gaining attention due to their involvement in various physiological and pathological processes, including inflammation, immunity, tumor progression, neurodegeneration, and cardiovascular diseases, among others.12 The cystatin family proteins inhibit cysteine proteases, particularly the cathepsin enzymes involved in lysosome protein breakdown.