KLK11 encodes a serine protease that functions as a multifunctional enzyme with tissue-specific roles in normal physiology and cancer progression. The protein exhibits serine-type endopeptidase activity and cleaves substrates preferentially after arginine residues 1. KLK11 exists in multiple alternatively spliced isoforms, including brain-type and prostate-type variants 2. In cancer contexts, KLK11 demonstrates complex, tissue-specific expression patterns with opposing prognostic implications. In prostate cancer, lower KLK11 expression correlates with higher tumor stage, Gleason score, and poor survival outcomes 32. Conversely, in ovarian cancer, KLK11 overexpression associates with poor prognosis 4, while in laryngeal cancer, KLK11-positive tumors show decreased risk of death 5. Functionally, KLK11 knockdown inhibits colorectal cancer cell proliferation and increases chemotherapy sensitivity through caspase-3 activation 6. In gastric cancer, KLK11 acts as a tumor suppressor by inhibiting mTOR/4E-BP1 signaling pathway, with miR-1304 negatively regulating its expression 7. The protein is widely expressed across multiple tissues and may play important roles in normal bronchial physiology 8.