Single-drug parenteral estrogen treatment in prostatic cancer: a study of two maintenance-dose regimens

Treatment of 17 patients with prostatic cancer with 320 mg polyestradiol phosphate (PEP) as intramuscular injections every fourth week suppressed serum testosterone (T) values to orchidectomy levels within 1 month, and serum estradiol-17 beta (E2) rose to a mean level of 2,456 pmol/liter after 6 months. Following 6 months of treatment, the PEP dose was reduced to 80 mg/4 weeks in 9 and 160 mg/4 weeks in eight patients. Mean T levels, increased significantly after dose reduction in both groups and were above the upper orchidectomy limit at 1 month after dose reduction in the 80 mg group. Mean T levels, however, remained below this level at 5 months in the 160 mg group. Dose reduction caused a rise in gonadotropin levels in the 80 mg but not in the 160 mg group. While 320 mg/4 weeks may be a suitable initial dosage, doses less than or equal to 160 mg/4 weeks are insufficient as maintenance dosages if orchidectomy values of T are required.