KLK4 and prostate cancer: In recent years, many kallikreins in addition to KLK3/PSA, such as KLK2, KLK4, KLK5, KLK6, KLK7, KLK8, KLK9, KLK10, KLK11, KLK13, and KLK15 were found to be candidate biomarkers for several endocrine-related malignancies, including breast, ovarian and prostate cancers, demonstrating the immense clinical applicability of this family (Diamandis and Yousef, 2002; Borgono and Diamandis, 2004).