Residual prostate cancer after radiotherapy: a study of radical cystoprostatectomy specimens

The incidence of histologic prostate cancer (CaP) after definitive radiation therapy (RT) for localized disease is rarely quantitated. We investigated the relationship between prostate-specific antigen (PSA) and histologically residual CaP after definitive RT in patients undergoing radical cystoprostatectomy (RCP) for unrelated indications.

We reviewed our prostate cancer database to identify patients undergoing RCP who previously received definitive RT for localized CaP. Pre-radiation variables examined include PSA, Gleason score, radiation modality, and dose. Post-radiation variables reviewed include PSA, time to RCP, the presence of histologically proven prostate cancer, and Gleason score.

We identified 21 patients who underwent RCP at a median of 60 months after RT for localized CaP. Pre-radiation Gleason scores were low (6 or less) to intermediate risk (3+4) in 82% (14 of 17), intermediate (4+3) to high (8 or greater) in 18% (3 of 17), and unavailable in 4 patients. Median pre-radiation PSA was 9 ng/mL. Median PSA before RCP in all patients was 0.8 ng/mL. A total of 52% (11 of 21) of patients demonstrated active CaP in the RCP specimen. Although 89% (16 of 18) of patients met the Phoenix definition of biochemical freedom from disease, 50% (8 of 16) of these patients had histologically residual CaP at the time of RCP. Median PSA was not significantly different between patients with and without active CaP.

Histologic evidence of CaP was noted in 50% of patients demonstrating biochemical freedom from disease at the time of RCP. Although the biological significance of active CaP in this select population is uncertain, our findings demonstrate the limitations of PSA in monitoring CaP disease activity after definitive RT.