KLK3 and cancer: The newly identified members of the kallikrein family are being intensively investigated for their utility as cancer biomarkers, in part because other previously identified members, namely prostate specific antigen (human kallikrein 3) (Diamandis, 1999) and human glandular kallikrein 2 (Rittenhouse et al, 1998), have been found to be particularly useful in this regard and in part because it is reasonable to postulate on biological grounds that proteases are important mediators of tumour invasion and metastasis (Woodhouse et al, 1997; Kleiner and Stetler-Stevenson, 1999; Matrisian, 1999).