Merkel cell carcinoma: two case reports focusing on the role of fluorodeoxyglucose positron emission tomography imaging in staging and surveillance.

BACKGROUND: Merkel cell carcinoma (MCC) is a rare skin neuroendocrine carcinoma frequently occurring in the head and neck area. It is known for being a locally aggressive disease with a high incidence of regional and distant metastases. Accurate initial staging and close surveillance are critical in the management of the disease.

METHODS AND RESULTS: Two cases of MCC are reported in which fluorine-18-fluorodeoxyglucose positron emission tomography (FDG PET) imaging has been beneficial in directing management and predicting clinical course. Pretreatment FDG PET scans detected metastatic disease in subcentimeter lymph nodes that were not appreciated in initial computed tomography images. Posttreatment FDG PET scans predicted response to therapy with the level of FDG uptake correlating in both areas of complete response to treatment and areas of residual diseases. Finally, FDG PET imaging also detected the progression of the disease after initial treatment.

CONCLUSION: FDG PET imaging is a very sensitive modality in staging, assessment of treatment response, and surveillance of MCC. Because of the rarity of MCC, multicenter study is warranted to accumulate enough cases to determine the sensitivity and specificity of FDG PET in staging and surveillance of MCC, and the impact on the management and treatment outcome.