[Post-radiotherapy cutaneous neuro-endocrine carcinoma]. / Carcinome neuro-endocrine cutané en zone irradiée.

INTRODUCTION: Merkel cell carcinoma or cutaneous neuroendocrine carcinoma is an uncommon severe disease. The carcinogenic effect of ionizing radiations has been suspected in exceptional observations. We report the sixth case of Merkel cell neuroendocrine carcinoma in a patient with prior radiotherapy. CASE REPORT: An 86-year-old man underwent radiotherapy for a basal cell carcinoma of the tip of the nose and developed a highly aggressive Merkel cell carcinoma at the same location 6 years later. DISCUSSION: The development of Merkel cell carcinoma on irradiated tissue accounts for 2.6 p. 100 of the 227 publications where dermatological history was reported. This percentage may be underestimated. The similar localizations of the irradiated zone and the site of cancer development 5 years later suggest that the Merkell cell carcinoma may be a radio-induced tumor. The delay may vary from 5 to 47 years. The similarity of the carcinogenic factors involved in Merkel cell carcinoma and squamous cell or basal cell carcinomas (ultraviolet, ionizing irradiation) and the frequent association of different types favor an epidermal origin for Merkel cell carcinoma. In clinical practice, past history of radiotherapy in an area where Merkell cell carcinoma develops indicates that therapeutic management must exclude post-operative radiotherapy.