[Circulating prostate cells and bone marrow micro-metastasis and not treatment modality determine the risk and time to biochemical failure in low risk prostate cancer.].

Introduction: Minimal residual disease (MRD) is that which persists after curative treatment for prostate cancer. It has the potential to grow and cause metastasis. The detection of circulating prostate cells (CPCs) and bone marrow micro-metastasis could represent different sub-types of MRD.

Objective: To determine biochemical failure free survival and time to failure, the presence of circulating prostate cells and bone marrow micro-metastasis in men treated for low risk prostate cancer.

Hypothesis: The presence of MRD and not the treatment modality determines the results of therapy.

Methods: Blood and bone marrow samples were taken one month after completing treatment to detect CPCs and micro-metastasis. Patients were classified into three groups; A: CPC negative, micro-metastasis negative, B: CPC negative, micro-metastasis positive and C: CPC positive. Biochemical failure was defined as a PSA >0.2ng/ml after radical prostatectomy and >2.0ng/ml post nadir after radiotherapy. After 10 years of follow up the Kaplan-Meier survival curve was determined and using a flexible adjusted parametric model the mean restricted survival time (MRST) was calculated for all groups.

Results: 343 men participated, 183 post surgery and 160 post radiotherapy, 181 (53%) had clinical stage T1 and 162 (47%) clinical stage T2a. There were no differences in treatment results between prostatectomy and radiotherapy. T1 patients had a significantly lower frequency of MRD than T2 patients (20% versus 67% p<0.001). Patients negative for MRD (Group A) had a 97% 10-year survival rate and a MRST to failure of 9.9 years. Men with only micro-metastasis (Group B) had a survival rate similar to Group A during the first five years, afterwards there was increasing treatment failure (late failure). Men positive for CPCs had a high risk of early failure.

Conclusions: The treatment results of surgery and radiotherapy are similar and depend on the sub-type of MRD. Men negative for MRD could be considered cured with a biochemical failure free survival of >95% at 10 years. The sub-type of MRD determines early or late failure and could be useful in the risk classification of patients after curative treatment.