The present invention describes a method for detecting castration-resistant prostate cancer (CRPC) in a patient afflicted with prostate cancer comprising (a) performing a direct analysis comprising immunofluorescent staining and morphological characterization of nucleated cells in a blood sample obtained from the patient to detect circulating tumor cells (CTC), (b) determining prevalence of a CTC subpopulation associated with CRPC comprising detecting a measurable feature of each biomarker in a panel of morphological and protein biomarkers, and (c) comparing the prevalence of said CTC subpopulation to a predetermined threshold value, wherein the prevalence of the CTC subpopulation associated with CRPC above said predetermined threshold value is indicative of CRPC. In some embodiments, the CTC subpopulation associated with CRPC comprises CK− CTCs. In some embodiments, the CTC subpopulation associated with CRPC comprises small CTCs. In additional embodiments, the methods of the invention further comprise molecular analysis of the CTCs.