Although
circulating tumor cell (CTC) enumeration in peripheral blood has already been validated as a reliable
biomarker in predicting prognosis in metastatic
castration-resistant
prostate cancer (mCRPC), patients with favorable CTC counts (CTC < 5/7.5 ml) still experience various survival times. Assays that can reduce patients' risks are urgently needed. In this study, we set up a real-time quantitative polymerase chain reaction (RT-qPCR) method to detect epithelial-mesenchymal transition (EMT) and stem cell gene expression status in peripheral blood to validate whether they could
complement CTC enumeration. From January 2013 to June 2014 we collected peripheral blood from 70 mCRPC patients and enumerated CTC in these blood samples using CellSearch system. At the same time, stem cell-related genes (ABCG2, PROM1 and PSCA) and EMT-related genes (TWIST1 and
vimentin) were detected in these peripheral blood samples using an RT-qPCR assay. Patient overall survival (OS) and treatment methods were recorded in the follow-up. For patients who received first-line
chemotherapy,
docetaxel plus
prednisone, PSA progression-free survival (PSA-PFS) and PSA response rate were recorded. At the time of analysis, 35 patients had died of
prostate cancer with a median follow-up of 16.0 months. Unfavorable CTC enumerations (CTC ≥5/7.5 ml) were predictive of shorter OS (p = 0.01). Also, positive stem cell gene expression indicated poor prognosis in mCRPC patients (p = 0.01). However, EMT gene expression status failed to show any prognostic value in OS (p = 0.78). A multivariate analysis indicated that
serum albumin (p = 0.04), ECOG performance status (p < 0.01), CTC enumeration (p = 0.02) and stem cell gene expression status (p = 0.01) were independent prognostic factors for OS. For the 40 patients categorized into the favorable CTC enumeration group, positive stem cell gene expression also suggested poor prognosis (p < 0.01). A combined prognostic model consisting of stem cell gene expression and CTC enumeration increased the concordance probability estimated value from 0.716 to 0.889 in comparison with CTC enumeration alone. For patients who received
docetaxel plus
prednisone as first-line
chemotherapy, positive stem cell gene expression suggested a poor PSA-PFS (p = 0.01) and a low PSA response rate (p = 0.008). However, CTC enumeration and EMT gene expression status did not affect PSA-PFS or PSA response rates. As a result, detection of peripheral blood stem cell gene expression could
complement CTC enumeration in predicting OS and
docetaxel-based treatment effects in mCRPC patients.