Disclosed herein are compositions and methods for detecting biological molecules and biomarkers associated with prostate cancer. Disclosed herein are compositions and methods for detecting biological molecules and biomarkers associated with castration-resistant prostate cancer wherein such biological molecules and biomarkers comprise androgen-receptor splice variants that can be used to develop effective therapeutic regimens for prostate cancer patients. Disclosed herein are methods of using biological molecules and biomarkers related to androgen-receptor splice variants for assessing therapeutic resistance to drugs such as enzalutamide and abiraterone.