KLK3 and posterior cortical atrophy: In addition, a subtype of metastatic castration-resistant PCa termed double-negative PCa, characterized by low androgen receptors (AR) and no neuroendocrine signaling, has increased DKK-1 relative to prostate-specific antigen (PSA), suggesting DKK-1 as a possible biomarker and pharmaceutical target for a substantial portion of PCa with low AR and PSA [40].