The presence of secondary circulating prostate tumour cells determines the risk of biochemical relapse for patients with low- and intermediate-risk prostate cancer who are treated only with external radiotherapy

INTRODUCTION: The classification of patients with prostate cancer is used to determine treatments based on risk factors. The presence of secondary circulating prostate tumour cells (CPCs) detected in peripheral blood after a curative treatment has been associated with a worse prognosis. We present a prospective study of CPC detection post radiotherapy and the oncological results. PATIENTS AND METHODS: All of the patients classified as low and intermediate risk that were treated with radiotherapy were included. Three months after finishing treatment, an 8-ml blood sample was taken to detect CPCs. Mononuclear cells were obtained using gel centrifugation, and CPCs were identified using immunocytochemistry with anti-prostate-specific antigen. Patients were classified as low-risk CPC positive or negative and intermediate-risk CPC positive or negative. The biochemical relapse-free survival analysis was determined based on a follow-up of up to 15 years using the Kaplan–Meier and Cox regression models. Biochemical failure was defined according to the Pheonix II criteria. RESULTS: Of 241 patients, 181 (75.1%) were classified as low risk and 60 (24.9%) as intermediate risk. Biochemical failure was observed in 27.1% (49/181) of the low-risk prostate cancer participants and in 53.3% (32/60) of intermediate-risk participants after 15 years of follow-up. 20.4% (37/181) of the low-risk cancer participants had detectable CPCs in comparison with 43.3% (26/60) of the intermediate-risk cancer participants (p < 0.001 overall risk 2.98, confidence interval (CI) 95% 1.59–5.56; relative risk 2.12, CI 95% 1.41–3.19). Positive CPC patients had a worse prognosis, and a shorter time period until biochemical relapse, regardless of risk group. The biochemical relapse-free survival curves show that intermediate-risk participants who were CPC negative had a higher survival rate and slower disease progression than those participants who were low risk but CPC positive. CONCLUSIONS: CPC detection is a risk factor for biochemical relapse and could be useful in identifying patients that will need additional treatment.