Detection of residual prostate cancer after external radiotherapy. Role of prostate specific antigen and transrectal ultrasonography.

BACKGROUND

Although the incidence of positive post-radiotherapy biopsies has been reported, the range is considerable (19-93%) and depends partly on patient-selection criteria. In addition, the prognostic significance of transrectal ultrasonography (TRUS) and prostate specific antigen (PSA) used alone and in combination in predicting residual cancer after radiotherapy has yet to be determined.

METHODS

Transrectal ultrasonography-guided prostate biopsies were performed on 31 unselected patients with prostate cancer 34-77 months (mean, 51 months) after definitive external beam radiotherapy was completed. Biopsy results were compared for pre- and posttreatment parameters (clinical stage, grade, PSA, and TRUS).

RESULTS

In 22 patients (71%), residual cancer was detected histologically by biopsy. All but one patient (12/13, 92%) with a pretherapy PSA value greater than 10 ng/mL had a positive biopsy compared with 50% of those (7/14) with a pretherapy PSA value less than or equal to 10 (P < 0.05). After radiotherapy, a positive biopsy was noted for 15 of 16 patients (94%) with a PSA value greater than 2 and in 20 of 23 (87%) of those with abnormal TRUS findings (P < 0.01 and P < 0.005, respectively).

CONCLUSIONS

The most clinically useful model for predicting histologically identifiable residual cancer was either a serum PSA value greater than 2 or a PSA value less than or equal to 2 and abnormal TRUS findings. The positive and negative predictive values of the model were 84% and 83%, respectively. The model predicted biopsy results correctly in 26 of 31 patients (84%). Transrectal ultrasonography is recommended as a diagnostic tool for patients whose PSA level ranges from a detectable level to less than or equal to 2 ng/mL.