KLK3 and cancer: The first clinically applicablecancer biomarker identified this way in 1965 was carcinoembryonicantigen (CEA) in colon cancer tissue,67,68 and by theend of the 1970s, potential serum tests had been developed for a varietyof cancers.68 Additional biomarkers developedin the 1980s included PSA, AFP, and cancer antigens 19-9 (CA19-9),72-4 (CA72-4), 125 (CA125), and 15-3 (CA15-3).69−74