RareCyte’s androgen receptor splice variant 7 (ARv7) and neuroendocrine marker, synaptophysin (SYP), circulating tumor cell assay provides highly accurate, repeatable, and precise results for circulating tumor cell count, ARv7 and SYP biomarker expression, and is suitable for use in large, multi-center clinical trials of prostate cancer. ARv7/Synaptophysin assay enables a blood-based investigation of two prominent mechanisms by which tumors become resistant to second line endocrine therapies.