Sister chromatid exchange in patients treated with methotrexate for psoriasis.

Sister chromatid exchange (SCE), which is considered a sensitive method in evaluation of mutagenicity and may be an indicator of carcinogenicity, was determined in lymphocytes from 8 patients with severe psoriasis who underwent treatment with oral methotrexate (MTX). During the treatment period (median 118 days, range 50-298 days) a significant increase in SCE compared to the pretreatment value was found in 1 patient only. It is concluded that no long-term damage as measured by SCE occurs in lymphocytes from psoriasis patients treated with MTX.