Phase II trial of hormonal cytoreduction with megestrol and diethylstilbestrol in conjunction with radiotherapy for carcinoma of the prostate: outcome results of RTOG 83-07.

Purpose: RTOG 83-07 is a Phase II randomized protocol designed to compare the efficacy and toxicity of Megestrol vs. Diethylstilbestrol (DES) used as cytoreductive agents prior to and during radiotherapy. The end points of this study include tumor clearance rate, effect on serum testosterone, loco-regional control, disease-free interval, and survival.
Methods and Materials: Eligible patients were those with histologically confirmed locally advanced adenocarcinoma, clinical Stage B2 (T2B) and C (T3) without regional lymph node involvement, or with lymph node involvement limited to the pelvis. Patients were stratified by clinical stage, histological grade, and nodal status, and were randomized to receive either Megestrol 40 mg three times per day by mouth, or Diethylstilbestrol 1 mg three times per day by mouth. The drugs were started 2 months prior to initiation of radiotherapy and were continued throughout the radiotherapy course. Radiotherapy consisted of 44-46 Gy, 1.8-2 Gy per day to the regional lymphatics, followed by a boost to the prostate consisting of 20-25 Gy, 1.8-2 Gy per day, to a total of 65-70 Gy. Serum testosterone levels were recorded throughout the treatment course. Tumor response was assessed clinically and radiographically (CT scan). From March 1983 through June 1986 a total of 203 patients were accessioned to the study; 198 were analyzable.
Results: Correlation of the incidence of drug-related toxicity and treatment arm assignment revealed a significantly higher incidence of complications in the Diethylstilbestrol (DES) arm. The most prominent were the differences in the incidence of gynecomastia (55% vs. 7%) and fluid retention (21% vs. 6%). The incidence of thromboembolic phenomena was comparable (8% vs. 5% in the Megestrol arm). Patients on the DES arm demonstrated a significantly greater median decrease in testosterone level. Correlation of the treatment arm assignment and the rate of tumor regression and the incidence of complete response revealed no significant difference between the arms. At 7 years, 16% of patients on the Megace arm and 21% of patients on the DES arm manifested evidence of local failure.
Conclusions: The results of the study indicate comparable efficacy (using tumor clearance as an end point) of DES and Megestrol. Although DES appears more effective in suppressing testosterone, it is also associated with a higher incidence of drug-related toxicity.