Kallikrein-related peptidases in prostate, breast, and ovarian cancers: from pathobiology to clinical relevance

Tissue kallikrein (KLK1) and kallikrein-related peptidases (KLK2-15) comprise a family of 15 highly conserved secreted serine proteases with similar structural characteristics and a wide spectrum of functional properties. Both gene expression and protein activity of KLKs are rigorously controlled at various levels via diverse mechanisms, including extensive steroid hormone regulation, to exert their broad physiological role. Nevertheless, deregulated expression, secretion, and function of KLK family members has been observed in several pathological conditions and, particularly, in endocrine-related human malignancies, including those of the prostate, breast, and ovary. The cancer-related abnormal activity of KLKs upon substrates such as growth factors, cell adhesion molecules, cell surface receptors, and extracellular matrix proteins facilitate both tumorigenesis and disease progression to the advanced stages. The well-documented relationship between KLK status and the clinical outcome of cancer patients has led to their identification as promising diagnostic, prognostic, and treatment response monitoring biomarkers for these complex disease entities. The main objective of this review is to summarize the existing knowledge concerning the role of KLKs in prostate, breast, and ovarian cancers and to highlight their continually evolving biomarker capabilities that can provide significant benefits for the management of cancer patients.