Abstract
BackgroundMerkel cell carcinoma (MCC) is an aggressive neuroendocrine skin tumor. Currently, 18F-fluoro-deoxy-glucose (18F-FDG) PET/CT is the functional imaging modality of choice. Few data are available on the use of 68Ga-somatostatin analogs. The aim of our study was to evaluate and compare the diagnostic performance of 18F-FDG and 68Ga-somatostatin analog PET/CT in MCC patients.ResultsFifteen patients (12 males, 3 females; median age 73 years; range 41–81 years) with histologically proven MCC (4 with unknown primary lesion) who underwent both 18F-FDG and 68Ga-somatostatin analog PET/CT for staging, re-staging, or treatment response assessment were retrospectively evaluated. Results of both studies were qualitatively analyzed and compared on a patient- and lesion-based analysis, using histology or clinical/radiological follow-up as reference standard for final diagnosis. According to final diagnosis, 8/15 patients had at least one MCC lesion and 7/15 had no evidence of disease. On a patient-based analysis, 18F-FDG and 68Ga-somatostatin analogs correctly classified as positive 8/8 (100% sensitivity) patients and as negative 6/7 (85.7% specificity) and 5/7 (71.4% specificity) patients, respectively, with no significant difference. On a lesion-based analysis, 18F-FDG detected 67/75 lesions (89%) and 68Ga-somatostatin analogs 69/75 (92%), with no significant difference. In four patients with unknown primary MCC, both tracers failed to identify the primary MCC site.ConclusionsOur preliminary data suggest that 18F-FDG and 68Ga-somatostatin analog PET/CT provide good and equivalent diagnostic performance, adding interesting insights into the complex MCC biology. However, these results do not suggest that 18F-FDG PET/CT should be replaced by 68Ga-somatostatin receptor imaging, which should be performed in addition, according to clinical indication, to the perspective of “personalized medicine.”
Highlights
Merkel cell carcinoma (MCC) is an aggressive neuroendocrine skin tumor
CT or CT scan should be performed as part of the initial work up of MCC to stage the disease [16], while according to the more recent National Comprehensive Cancer Network (NCCN) guidelines, 18F-FDG PET/CT may be preferred to CT [17]
18F-FDG PET/CT was the first imaging of choice for evaluating MCC, according to current international guidelines [17]
Summary
Merkel cell carcinoma (MCC) is an aggressive neuroendocrine skin tumor. Currently, 18F-fluorodeoxy-glucose (18F-FDG) PET/CT is the functional imaging modality of choice. Merkel cell carcinoma (MCC) is a rare highly aggressive skin tumor, with a quickly increasing incidence rate over the last 20 years. It is characterized by neuroendocrine features such as somatostatin receptor expression, besides a Currently, the optimal imaging algorithm of MCC is not yet defined [6, 7]. A direct comparison between 18F-FDG and 68Ga-somatostatin receptor imaging (68Ga-SRI) PET/CT in the same MCC patient has been only reported in a few case reports [25,26,27] In this regard, potential interesting insights into tumor biology could derive from a head-to-head comparison of both tracers, besides possible implications in the perspective of a personalized patient management
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