PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No prior isotretinoin Endocrine therapy: Not specified Radiotherapy: Not specified Surgery: Not specified Other: No prior warfarin or its derivatives At least 3 months since megadose vitamin A (greater than 25,000 IU/day) or beta-carotene greater than 30 mg/day or alpha-tocopherol at least 400 IU daily No concurrent megadose vitamin A (greater than 25,000 IU/day), beta-carotene greater than 30 mg/day, alpha-tocopherol at least 400 IU daily, or other daily supplements and tonics