Kallikrein-related peptidase 3, more commonly known as Kallikrein 3 (KLK3) or Prostate-Specific Antigen (PSA), is a serine protease belonging to the kallikrein family. Its primary function is to cleave proteins, and it is a key biomarker for prostate cancer. Secreted by the epithelial cells of the prostate gland, elevated levels of KLK3 in the blood are often indicative of prostate pathologies, including benign prostatic hyperplasia and prostate cancer. Beyond its role as a diagnostic marker, recent research explores its potential as a therapeutic target in cancer treatment. Its unique expression pattern and enzymatic function make it a subject of extensive research in oncology.