DISEASE CHARACTERISTICS: Diagnosis of psoriasis, cutaneous disorders of keratinization, or other retinoid-responsive disorders or malignancies OR Diagnosis of multiple basal cell carcinomas resulting from one of the following: Nevoid basal cell carcinoma syndrome Xeroderma pigmentosum Arsenical insecticide exposure Sunlight exposure X-irradiation Widespread involvement (e.g., psoriasis involving 10% or more of body surface area OR Severe, recalcitrant localized involvement (e.g., keratoderma palmaris et plantaris) Female patients must have disease that is severe and recalcitrant to all other standard therapies

PATIENT CHARACTERISTICS: Age: Any age Performance status: Not specified Life expectancy: Not specified Hematopoietic: Not specified Hepatic: No persistently abnormal liver function tests SGOT or SGPT no greater than 3 times upper limit of normal (ULN) Renal: No persistently abnormal renal function tests Creatinine no greater than 3 times ULN Other: No persistent pretreatment hypertriglyceridemia (greater than 300 mg/dL) No significant neurological, musculoskeletal, or other internal medical disorder that would preclude retinoid therapy Not pregnant Negative pregnancy test Fertile patients must use effective contraception during and for 3 years after study

PRIOR CONCURRENT THERAPY: No chronic intake of excessive vitamin A exceeding 25,000 IU/day