A method comprising: a. capturing circulating cancer cells from a sample from a test subject; b. extracting mRNA to provide a RNA sample; and c. detecting and quantifying each of full-length androgen receptor (AR-FL), androgen receptor variant 7 (AR-V7), and androgen receptor variant 5,6,7 (AR-V567) in parallel digital droplet PCR assays; wherein: (i) the parallel digital droplet PCR assay(s) for detecting and quantifying for AR-FL optionally comprises the following set of primers or probes: a primer according to the sequence as set forth in SEQ ID NO: 7 and a primer according to the sequence as set forth in SEQ ID NO: 8, and optionally a probe according to the sequence as set forth in SEQ ID NO: 9; (ii) the parallel digital droplet PCR assay(s) for detecting and quantifying for AR-V7 comprises the following set of primers or probes: a primer according to the sequence as set forth in SEQ ID NO: 11 and a primer according to the sequence as set forth in SEQ ID NO: 12, and optionally a probe according to the sequence as set forth in SEQ ID NO: 13; and (iii) the parallel digital droplet PCR assay(s) for detecting and quantifying for AR-v567es optionally comprises the following set of primers or probes: a primer according to the sequence as set forth in SEQ ID NO: 15 and a primer according to the sequence as set forth in SEQ ID NO: 16, and optionally a probe according to the sequence as set forth in SEQ ID NO: 17. a. capturing circulating cancer cells from a sample from a test subject; b. extracting mRNA to provide a RNA sample; and c. detecting and quantifying each of full-length androgen receptor (AR-FL), androgen receptor variant 7 (AR-V7), and androgen receptor variant 5,6,7 (AR-V567) in parallel digital droplet PCR assays; wherein: (i) the parallel digital droplet PCR assay(s) for detecting and quantifying for AR-FL optionally comprises the following set of primers or probes: a primer according to the sequence as set forth in SEQ ID NO: 7 and a primer according to the sequence as set forth in SEQ ID NO: 8, and optionally a probe according to the sequence as set forth in SEQ ID NO: 9; (ii) the parallel digital droplet PCR assay(s) for detecting and quantifying for AR-V7 comprises the following set of primers or probes: a primer according to the sequence as set forth in SEQ ID NO: 11 and a primer according to the sequence as set forth in SEQ ID NO: 12, and optionally a probe according to the sequence as set forth in SEQ ID NO: 13; and (iii) the parallel digital droplet PCR assay(s) for detecting and quantifying for AR-v567es optionally comprises the following set of primers or probes: a primer according to the sequence as set forth in SEQ ID NO: 15 and a primer according to the sequence as set forth in SEQ ID NO: 16, and optionally a probe according to the sequence as set forth in SEQ ID NO: 17. (i) the parallel digital droplet PCR assay(s) for detecting and quantifying for AR-FL optionally comprises the following set of primers or probes: a primer according to the sequence as set forth in SEQ ID NO: 7 and a primer according to the sequence as set forth in SEQ ID NO: 8, and optionally a probe according to the sequence as set forth in SEQ ID NO: 9; (ii) the parallel digital droplet PCR assay(s) for detecting and quantifying for AR-V7 comprises the following set of primers or probes: a primer according to the sequence as set forth in SEQ ID NO: 11 and a primer according to the sequence as set forth in SEQ ID NO: 12, and optionally a probe according to the sequence as set forth in SEQ ID NO: 13; and (iii) the parallel digital droplet PCR assay(s) for detecting and quantifying for AR-v567es optionally comprises the following set of primers or probes: a primer according to the sequence as set forth in SEQ ID NO: 15 and a primer according to the sequence as set forth in SEQ ID NO: 16, and optionally a probe according to the sequence as set forth in SEQ ID NO: 17.