OBJECTIVES: To determine the frequency of primary circulating prostate cells in men with prostate cancer at the time of diagnosis, the association with micrometastasis, sub-classification for CD82 and the relation with pathological stage. To determine their clinical usefulness to identify patients in whom radical prostatectomy would be first choice therapy.METHODS: Men with the diagnosis of prostate cancer before definitive therapy. Blood and bone marrow samples were taken, mononuclear cells separated by differential centrifugation and prostate cells identified with immunocytochemistry using anti-PSA. Positive samples were sub-classified with anti-CD82. Details of serum PSA, Gleason score and pathological stage were registered. RESULTS: Of 77 men 58 (75.3%) had primary CPCs detected, there was an association with stage but not Gleason. 31 (40.3%) had micrometastasis with an association with stage and Gleason score. CPC-negative patients had fewer micrometastasis detected, 1/19 versus 30/58 (p<0.003).There was an inverse relation between CD82 expression and Gleason score, men with CPCs expressing CD82 had fewer micrometastasis. The combined group of CPC negative and CPC positive CD82 positive men showed a sensitivity of 87% and specificity of 73.9% for the absence of micrometastasis.CONCLUSIONS: The detection of CPCs and sub-classification with CD82 could be clinically useful to identify men with a significantly lower risk of micrometastais and as a consequence to identify men in whom radical prostatectomy could be the best initial treatment.