Role of nuclear medicine in staging and management in a case of Merkel cell carcinoma.

Merkel cell carcinoma (MCC) is a rare, aggressive, cutaneous neuroendocrine neoplasm, the presentation of which varies. Histologically it is a dermic lesion. Differentiation of the cells is difficult to distinguish from cutaneous metastases of neuroendocrine carcinomas, melanoma and angiosarcoma. The immunohistochemical profile of MCC and its ultrastructural characteristics help to differentiate this carcinoma from other neoplasms. The pathogenesis of MCC is uncertain. Despite having been associated with different chromosomic abnormalities and apoptotic mechanisms, solar exposure and immunosuppression have been included among the causes of this disease.1 Compared to other imaging techniques, 18F-FDG PET is a good diagnostic tool for the staging of patients with MCC mainly because a whole body image may be obtained with only one scan. However, a negative PET does not exclude the absence of disease.1,2 On the other hand, it seems that the use of selective biopsy of the sentinel lymph node (SLN) in these patients has great potential applicability. Nonetheless, few cases using this technique have been described in the literature.3 A 71-year-old womanwith cutaneous lesions suspected of MCC in the left buttock (Fig. 1)was referred for study. Taking intoaccount that the tumor is predisposed to lymph node and hematogenous dissemination, whole body 18F-FDG PET-CT was considered to be the best strategy to rule out disseminated disease which contraindicates determined therapeutic approaches. If negative, surgery would be performed with extraction of the SLN. The 18FFDG PET-CT study only demonstrated the presence of a primary lesion in the left buttock with a low metabolic rate and no distant tumoral involvement (Fig. 2A). Tumor resection was carried out