Human tissue kallikreins (hKs) are attracting increased attention owing to their 
association with various forms of cancer and other diseases. Human tissue 
kallikrein genes represent the largest contiguous group of proteases within the 
human genome. There are many areas of kallikrein research that need to be 
further explored, including their tissue expression patterns, their regulation, 
identification of specific substrates, their participation in proteolytic 
cascades, and their clinical applicability as cancer biomarkers and therapeutic 
targets. In this review, we briefly describe the current status of kallikrein 
research and identify future avenues that will enhance our understanding of 
their function and involvement in human diseases.