Merkel cell carcinoma in organ‐transplant recipients: report of two cases with unusual histological features and literature review

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Abstract
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. 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. 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. 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.