Early stage prostate cancer treated with radiation therapy: Stratifying an intermediate risk group

Abstract

This study identifies two early prostate cancer populations within the T1/T2AB, Gleason 2-7, pretreatment prostate specific antigen (PSA) 4-15 ng/ml grouping. By demonstrating different outcomes we may be able to more appropriately select a subgroup for whom adjuvant therapy trials or altered treatment techniques are indicated. One hundred forty-six patients with T1/T2AB, Gleason score 2-7, PSA 4-15 ng/ml prostate cancer were treated with external beam radiotherapy alone from November 1987 to October 1993. The median pretreatment PSA was 8.6 and the mean 8.7. Minimum follow-up was 2 years with a median of 38 months (mean 42 months, range 24-87). The median age was 70 years (range 58-83) and the median central axis dose delivered was 7240 cGy (mean 7273, range 6541-7895 cGy). Eleven patients received conventional radiotherapy while 135 were treated using conformal techniques. As there is evidence that a low PSA nadir is an early marker for long term biochemical control, time to post treatment PSA < 1 ng/ml was actuarially analyzed by Gleason score, pretreatment PSA, radiation dose, stage, and the presence of perineural invasion. Pretreatment PSA was the only patient characteristic predictive of achieving a PSA level < 1.0 ng/ml. Biochemical relapse free (bNED) control (non rising PSA) was then compared for patients above and below the approximate median pretreatment PSA level of 8 ng/ml. bNED control rates and the time to PSA < 1.0 ng/ml were estimated using Kaplan-Meier methodology, and differences in bNED control and PSA < 1.0 ng/ml according to PSA level were evaluated using the log-rank test. Results from actuarial analysis revealed that pretreatment PSA was the only significant variable predictive of a PSA < 1.0 ng/ml. Ninety-eight percent of patients with pretreatment PSA < 8 achieved a PSA level < 1.0 ng/ml within 3 years compared to 78% for patients with a PSA > 8 ng/ml (p = 0.0003). bNED control for the two groups separated at a pretreatment PSA of 8 ng/ml confirms a favorable outcome, 88% bNED control at 5 years for < 8 ng/ml and 74% for a pretreatment PSA > or = 8 ng/ml (p = 0.007 for overall curve comparison). For early prostate cancer patients (T1/T2AB, Gleason 2-7, pretreatment PSA 4-15) there is a significant break in bNED control following external beam radiation at a pretreatment PSA level of 8 ng/ml. Patients with pretreatment PSA < 8 have a very favorable bNED response with radiation alone while those with a pretreatment PSA 8-15 have a significant decrease in bNED response. The 27% failure rate at 5 years in the PSA 8-15 ng/ml patients may justify altered treatment techniques or clinical trials of adjuvant androgen deprivation in this group.