Human tissue kallikreins (hKs), which are encoded by the largest contiguous 
cluster of protease genes in the human genome, are secreted serine proteases 
with diverse expression patterns and physiological roles. Although primarily 
known for their clinical applicability as cancer biomarkers, recent evidence 
implicates hKs in many cancer-related processes, including cell-growth 
regulation, angiogenesis, invasion and metastasis. They have been shown to 
promote or inhibit neoplastic progression, acting individually and/or in 
cascades with other hKs and proteases, and might represent attractive targets 
for therapeutic intervention.