This work defined five subclasses of mCRPC: uniformly AR-expressing tumors with no neuroendocrine features (ARPC), tumors with weak or diffuse AR expression and no neuroendocrine features (AR-low prostate cancer, or ARLPC), tumors expressing both AR and neuroendocrine markers (amphicrine prostate cancer or AMPC), AR-negative tumors with neuroendocrine features (small cell/neuroendocrine prostate cancer, or SCNPC), and tumors that exhibit neither AR expression nor small-cell neuroendocrine features (double-negative prostate cancer or DNPC) (46). This evidence concerns the gene AR and prostate cancer.