Table 2.

Criteria list used to assess the methodological quality of the studies

Quality item	Positive score
Was the spectrum of patients representative of the patients who will receive the test in practice?	Patients with histologically confirmed metastatic cancer, in whom medical history, physical examination, full blood count, basic biochemistry battery, urinalysis, stool occult blood testing, immunohistochemistry with specific markers as well as imaging technology with chest X-ray, computed tomography of the chest abdomen and pelvis or mammography and MR imaging in certain cases failed to detect the primary tumor, were included
Were selection criteria clearly described?	It was clear how patients were selected for inclusion
Is the reference standard likely to correctly classify the target condition?	Histopathological analysis of tissue obtained by biopsy or surgery, or imaging procedures or clinical follow-up if no histopathological proof could be obtained
Did the whole sample, or a random selection of the sample, receive verification using a reference standard of diagnosis?	All patients, or a random sample of patients who underwent FDG-PET/CT, also underwent the reference standard
Was the reference standard independent of the index test (i.e., the index test did not form part of the reference standard)?	FDG-PET/CT did not form part of the reference standard
Was the execution of the index test described in sufficient detail to permit replication of the test?	All of the following parameters were described:
	-Time of fasting before FDG administration, FDG dose, time interval between FDG administration and scanning
	-Application of intravenous and/or oral CT contrast
	-Scanned area
	-Evaluated images (AC and/or nAC)
	-Interpreter(s) of FDG-PET/CT mentioned
Was the execution of the reference standard described in sufficient detail to permit replication?	Besides histopathological analysis of FDG-PET/CT positive findings, additional diagnostic procedures (e.g., gastroscopy, CT, MR imaging) and duration of follow-up were described, if applicable
Were the index test results interpreted without knowledge of the results of the reference standard?	FDG-PET/CT was interpreted without knowledge of the findings of the reference standard
Were the same clinical data available when test results were interpreted as would be available when the test is used in practice?	Interpreter(s) of FDG-PET/CT was/were aware of the histologic nature of the metastases of unknown primary
Were uninterpretable/intermediate test results reported?	All FDG-PET/CT results, including uninterpretable/ indeterminate/intermediate were reported
Were withdrawals from the study explained?	It is clear what happened to all patients who entered the study
Was comparator review bias avoided?	Blinding FDG-PET/CT to the other imaging modality, if more than one imaging modality was applied

AC: attenuation-corrected images

nAC: non-attenuation-corrected images

CT: computed tomography

FDG-PET: ¹⁸F-fluoro-2-deoxyglucose

FDG-PET/CT: ¹⁸F-fluoro-2-deoxyglucose positron emission tomography/computed tomography

MR: magnetic resonance