Cathepsin L is a lysosomal cysteine protease involved in intracellular protein degradation and turnover. It plays a key role in antigen processing, where it helps generate peptide fragments for presentation on MHC class II molecules, contributing to immune response regulation. In pathological conditions, elevated Cathepsin L activity is associated with tumor invasion and metastasis, as it degrades extracellular matrix components such as collagen and laminin, facilitating cancer cell migration. It is also implicated in inflammatory diseases and tissue remodeling processes, including arthritis and atherosclerosis. Due to its involvement in disease progression, Cathepsin L is being studied as a potential biomarker and therapeutic target, particularly in cancer and neurodegenerative disorders where protein aggregation occurs. Inhibitors of Cathepsin L are under investigation for their ability to slow tumor growth and reduce tissue damage in chronic inflammatory conditions.