KLK3 and cancer: Some of the United States of America Food and Drug Administration (FDA)-approved protein markers for cancer diagnosis include prostate-specific antigen (PSA), Pro2PSA, alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA), nuclear mitotic apparatus protein (NuMA, NMP22), and cancer antigens (CA-125, CA15-3, CA19-9) [145].