Positron Emission Tomography in Merkel Cell Carcinoma

SIMPLE SUMMARY: There is currently no consensus on a widely accepted algorithm for imaging Merkel cell carcinoma (MCC) patients. Baseline, tomographic imaging is not generally recommended in early-stage disease, but its value in locally advanced and/or distant metastatic MCC has been well established. In this context, the hybrid imaging modality positron emission tomography/computed tomography (PET/CT) is increasingly applied in the workup of metastatic or unresectable MCC, providing essential information for staging, restaging, and treatment monitoring of the disease. Although the role of PET/CT in the management of loco-regional MCC is still limited and less well-defined, current evidence suggests its important contribution also in cases of localized MCC. Herein, we provide a structured literature review summarizing the most important studies on the role of PET or PET/CT with different radiopharmaceuticals in the clinical care of MCC. ABSTRACT: Merkel cell carcinoma (MCC) is a rare neuroendocrine skin malignancy usually arising as a nonspecific nodule on sun-exposed areas of the head and neck. Given the poor prognosis of this aggressive tumor, assessment of disease burden in pre- and post-treatment care may ensure an optimal management with significant implications for patient surveillance and prognosis. Although imaging has established its role in locally advanced or distant metastatic MCC, a standard imaging algorithm is yet to be determined and respective recommendations are mainly based on melanoma. Positron emission tomography/computed tomography (PET/CT) is increasingly evolving as a valuable imaging tool in metastatic or unresectable MCC, mostly utilizing the glucose analogue (18)F-fluorodeoxyglucose ((18)F-FDG) as a radiotracer. Despite being inferior in detecting the disease in its early stages compared to the “gold standard” of sentinel lymph node biopsy, recent evidence suggests an important role for (18)F-FDG PET/CT in the routine workup of localized MCC. Moreover, (68)Ga-labeled somatostatin analogues have been employed as PET tracers in the field of MCC with promising, yet comparable to (18)F-FDG, results. This article provides a structured literature review of the most important studies investigating the role of PET or PET/CT in the clinical practice of MCC.