DISEASE CHARACTERISTICS: Diagnosis of actinic keratosis At least 3 clinically visible lesions on each lower posterior forearm Lesions must be discrete and quantifiable No prior or concurrent skin cancer on forearms Prior skin cancer (other than melanoma) on an area other than the forearms allowed unless chronic recurrent lesions indicate immunosuppression Concurrent skin cancer on an area other than the forearms allowed if active lesion previously excised

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Not specified Life expectancy: Not specified Hematopoietic: Not specified Hepatic: Not specified Renal: Not specified Other: No serious concurrent illness No immunosuppression due to medication or disease No invasive cancer (including melanoma) within the past 5 years Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception at least 28 days prior to and during study

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: At least 5 years since prior systemic chemotherapy At least 6 months since prior fluorouracil (5-FU) to forearms Prior or concurrent 5-FU to the face allowed Endocrine therapy: Not specified Radiotherapy: Not specified Surgery: See Disease Characteristics Other: At least 30 days since prior megadoses of vitamins (e.g., more than 400 IU of vitamin E, 200 micrograms of selenium, or 1 g of vitamin C per day or more than the tolerable upper limits of any other supplement) At least 6 months since prior tretinoin to forearms Prior or concurrent tretinoin to the face allowed No concurrent mega-doses of vitamins No other concurrent investigational drug or device