KLK3 and prostate cancer: One such test, the blood-based Stockholm3 test, combines patient age, previous prostate biopsy results, family history of prostate cancer, single-nucleotide variations (formerly single-nucleotide polymorphisms), and levels of total PSA, free PSA, human kallikrein 2, β-microseminoprotein, and growth differentiation factor 15 to estimate the risk of clinically significant cancer (Gleason score ≥3 + 4).