Background. Organ transplant recipients receiving immunosuppressive treatment are prone to skin carcinomas on sun‐exposed areas, and the frequency of such carcinomas in the long term reaches 40%. These carcinomas primarily are squamous cell carcinomas (SCC), which often are preceded by viral warts and premalignant keratoses. Human papillomaviruses (HPV) with other cocarcinogenic factors have been reported to play a role in the development of carcinomas in these patients. Methods. Five hundred renal‐graft recipients referred to our department were examined for the presence of warts, precancerous keratoses, Bowen disease, keratoacanthomas, and basal and squamous cell carcinomas. Adequate material for histologic and virologic examination was obtained from 24 patients. An in situ molecular hybridization technique was performed using biotinylated DNA probes for HPV types 1a, 2a, 5, 16, and 18 under stringent conditions. Results. HPV DNA was detected in 44 of 86 specimens, including 14 of 17 warts, 4 of 17 premalignant keratoses, 1 of 4 Bowen disease lesions, 8 of 12 keratoacan‐thomas, 3 of 4 tumors in which distinction between keratoacanthomas and SCC was difficult, and 14 of 30 SCC. Twenty‐six of 44 positive specimens contained several HPV types, whereas 30 specimens contained oncogenic types. Benign types 1 or 2 were detected alone in five SCC. HPV types 16 and 18 (usually detected in genital lesions) were found in 26 samples from sun‐exposed areas. Conclusions. Our results show that oncogenic and benign HPV often are detected within premalignant keratoses and SCC in organ transplant recipients, which suggests that HPV may play a role in the development of cutaneous malignancies.

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