Skin cancer after renal transplantation: the causal role of azathioprine.

In 167 unselected patients with renal allografts, after a lag of 3.5 years the prevalence of dysplastic keratotic lesions increased linearly by 6.8%/yr and number of lesions also increased. There was no relationship to sun exposure or skin type. Malignancies occurred in 5 patients after 9 years. Viral warts occurred in 42% but prevalence and extent were not related to time after transplantation or keratoses. Comparison with other drugs and diseases suggests malignant keratoses are initiated in two stages by the cytotoxic effect of azathioprine, the role of immunosuppression remaining unproved. Psoriasis and eczema remitted and the prevalence of zoster and fungal disease increased. P. orbiculare (but not P. ovale) infection increased, unlike in other states of immunosuppression, suggesting the organisms are distinct, not transitional, and differently influenced by the different immunodeficient states induced by drugs and disease.