PRIOR CONCURRENT THERAPY: Biologic therapy: No prior bone marrow transplant No concurrent tamoxifen for cancer treatment or prophylaxis Chemotherapy: Greater than 4 weeks since prior chemotherapy No concurrent cytotoxic chemotherapy Endocrine therapy: Greater than 4 weeks since prior hormonal therapy for cancer No concurrent prednisone No concurrent hormonal therapy for cancer treatment or prophylaxis Radiotherapy: Greater than 4 weeks since prior radiotherapy Surgery: Greater than 4 weeks since prior major surgery No prior solid organ transplant Other: At least 4 weeks since prior topical medications (e.g., tretinoin, isotretinoin, psoralen ultraviolet light therapy, or fluorouracil) for skin cancer No concurrent antiseizure medication