KLK3 and cancer: With regards to patients with PSA (“biochemical”) relapse and with a long doubling time of the PSA (PSADT) >12 months before they undergo a 68Ga-prostate-specific membrane antigen positron emission tomography/computed tomography (68Ga-PSMA PET/CT) scan, and with cancers that have a low International Society of Pathology (ISUP) grade 1, few given salvage treatment progress to metastatic disease and cancer-specific death [1,2,5,6,7,8].