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Background: Non-melanoma skin cancers are the commonest malignancies after organ transplantation and are often associated with human papillomavirus (HPV). Merkel cell carcinoma is an uncommon neuroendocrine skin tumor, of which 67 cases have been reported up till now, usually briefly, in organ transplant patients., Methods: Among a cohort of 2340 organ-transplant recipients, two patients (one renal, one heart) developed cutaneous Merkel cell carcinomas 5 and 12 years of post graft, respectively. These were studied histologically and immunohistochemically, as well as virologically for the presence of HPV. A thorough literature review of all reported cases of Merkel cell carcinoma following solid organ transplantation was performed., Results: Despite a typical immunophenotype, the tumors showed unusual histological features: both were epidermotropic, and one was intermingled with a bowenoid squamous cell carcinoma. Search for HPV by immunohistochemistry and PCR proved negative in both cases., Conclusion: In the setting of organ transplantation, Merkel cell carcinoma is much rarer than other non melanoma skin cancers but may show unusual histologic features. HPV do not seem to be involved in its pathogenesis.

Nm23 is a gene with a putative metastasis-suppressor function, whose expression is inversely correlated with the metastatic potential of some solid malignancies. Because very few data exist concerning the role of nm23 in skin tumors, we studied the immunohistochemical expression of nm23 gene product in frozen sections of normal skin and of 104 cutaneous benign or malignant, epithelial and mesenchymal tumors. Nm23 was found expressed within basal cells of the epidermis and its appendages. All basal cell carcinomas showed diffuse immunoreactivity predominating within cells located at the periphery of tumor masses; in contrast, most squamous cell carcinomas, premalignant lesions and the benign epithelial lesions studied showed very weak, if any, immunoreactivity. Benign nevi and most malignant melanomas expressed nm23 immunoreactivity and the pattern observed was similar between primary and metastatic lesions. These results show that nm23 is differentially expressed in cutaneous tumors. It seems likely that the strong immunoreactivity of basal cell carcinomas, contrasting with the almost non-expression in squamous cell carcinomas, reflects the different metastatic potential of these two types of tumors. In melanomas, no direct correlation between the metastatic phenotype and nm23 expression could be detected. Our results suggest that the nm23 gene is involved in cutaneous carcinogenesis; its precise role deserves further study.

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 keratoacanthomas, 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.