KLK3 and cancer: Cannabis use was reported to have a significant negative association with two forms of cancer (i.e., cannabis use was lower in those diagnosed with cancer): head and neck squamous cell carcinoma (non-medical use; case-control study) [129] and prostate cancer in older African American men, diagnosed with prostate-specific antigen levels (use type not reported; cross-sectional study; n = 644) [143].