Table 2.

Summary of the published studies (including >1 patient) presenting a direct comparison between ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET or ¹⁸F-FDG PET/CT and CT in Merkel cell carcinoma (in chronological order).

Author (Year)	No. of Patients Undergoing PET/No. of Patients Undergoing CT	Main Findings
Yao et al. (2005) [15]	2/2	Pre-treatment PET detected metastatic disease in both patients not appreciated in CT.
Peloschek et al. (2010) [20]	16/16	PET: Sensitivity 85.7%, specificity 96.2% Morphological imaging (CT, MRI, US): Combined sensitivity 95.5%, combined specificity 89.1%.
Maury et al. (2011) [21]	15/15	PET: Sensitivity 89%, specificity 100%, PPV 100%, NPV 93%. CT: Sensitivity 89%, specificity 100%, PPV 100%, NPV 93%.
Colgan et al. (2012) [23]	33/69	PET and PET/CT: Sensitivity 83%, specificity 95%, PPV 91%, NPV 91% in detecting nodal basin disease. CT: Sensitivity 47%, specificity 97%, PPV 94%, NPV 68% in detecting nodal basin disease. PET was significantly more sensitive and equally specific in comparison with CT.
Hawryluk et al. (2012) [24]	97/97	Bone/bone marrow metastases in 10 cases were revealed only on PET with no CT correlate.
George et al. (2014) [28]	23/n.r.	All lesions identified by CT were also detected by PET. Lesions not detected clinically or by conventional imaging (not further specified) were found in 44% of PET/CTs performed at initial presentation and subsequent monitoring with, respectively, 50% and 41% of scans identifying new lesions.
Poulsen et al. (2017) [34]	58/58	PET led to upstaging in 15 (25.9%) of patients, with no cases of downstaging. Upstaging was due to detection of distant metastases (4 cases) or regional nodes (6 cases) that were not reported on CT.
Singh et al. (2020) [10]	352/231	PET/CT upstaged patients (16.8% of 352) significantly more often than CT alone (6.9% of 231).

US, ultrasound; PPV, positive predictive value; NPV, negative predictive value; n.r., not reported.