Phase II study of low dose (LD) and high dose (HD) premarin in androgen independent prostate cancer (AIPC)

Abstract

4560 Background: Estrogens, including DES, transdermal estradiol, estramustine and PC-SPES, have shown antitumor activity in AIPC. We tested two doses of Premarin to determine efficacy and safety of this commonly available estrogen. Methods: Patients with progressive AIPC were eligible. Prior estrogen use, significant cardiac or thromboembolic disease, and concurrent steroids were not allowed. Patients were randomized to Premarin 1.25 mg once (LD) or 3 times (HD) daily. Prophylactic breast irradiation was encouraged and warfarin 1 mg daily was required, unless contraindicated. After the first stage of accrual, the LD arm was closed because of limited activity, while the HD arm continued to the 2nd stage. Results: 46 patients were enrolled; 17 patients were randomized to LD Premarin, 29 patients assigned to HD Premarin by randomization or direct assignment. One patient withdrew consent prior to therapy. Median follow up is 5.3 months. Median age was 69 years (range 52–86) and median PSA 84.6 ng/ml (range 2.5–794.1). 19 patients (41%) had measurable disease. PSA declines ≥ 50% were seen in 0% (95% C.I., 0–19.5) and 32.1% (95% C.I., 15.9–52.4) of patients treated with LD and HD premarin. 1 patient treated with HD Premarin had a partial measurable response (8.3%; 95% C.I., 0.2–38.5). Median time to progression was 3.3 and 3.2 months in the LD and HD arms, respectively. Premarin was well tolerated in 45 evaluable patients. One grade 4 toxicity was noted, a stroke in the LD arm. Grade 3 toxicity was rare with 1 allergic reaction, 2 DVTs and 3 episodes of GI toxicity in one patient. Two patients experienced grade 3 elevations in PT requiring modification of warfarin dose. No significant gynecomastia was reported. Analysis of serially drawn hormone levels and molecular correlates of treatment response is pending. Conclusions: HD Premarin is associated with a 32.1% PSA response rate, while no responses were seen with LD Premarin. A measurable response was noted in 1 of 12 patients treated with HD Premarin. Toxicity was modest, though thromboembolism was seen even with prophylactic warfarin. Ongoing studies are evaluating molecular and clinical predictors of response. No significant financial relationships to disclose.