PET evaluation of therapeutic limb perfusion in Merkel's cell carcinoma.

An 87-yr-old woman diagnosed with recurrent Merkel's cell carcinoma was treated with therapeutic limb perfusion and underwent PET scanning with 18F-fluorodeoxyglucose (FDG). PET studies were obtained before and after treatment to determine the response to the intervention. A baseline whole-body study was obtained to assess the extent and degree of disease activity. This was followed by a repeat PET scan 2 mo. later after treatment with isolated limb chemotherapy with high-dose melphalan and tumor necrosis factor-alpha. The initial scan demonstrated multiple foci of high FDG uptake in the left calf, a left supraclavicular lesion and also detected concurrent keratinizing squamous cell metastasis in the right axilla. A repeat PET study showed complete metabolic resolution of the lesions in the left calf after treatment. FDG PET may be a useful technique for staging Merkel cell carcinoma and for assessing the tumor response after therapy of this rare tumor.