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Quartuccio et al. J Cancer Metastasis Treat 2021;7:14 I http://dx.doi.org/10.20517/2394-4722.2020.118 Page 7 of 13

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Figure 4. Forest plot of per-lesion-based DR of F-FDG PET/CT for bone metastases.
In the per-lesion analysis (including 290 metastases out of 1038 suspicious lesions; 5 studies), PET/CT
showed a pooled SS of 86.3% (95%CI: 73.5%-93.5%) and SP of 93.4% (95%CI: 71.7%-98.8%) in the detection
of hematogenous metastases [Figure 7], with 10 FP and 66 FN findings. Substantial heterogeneity was
2
found for both SS (I = 72.04) and SP (I = 82.02%).
2
When restricting the analysis to bone metastases (3 articles, with 170 metastatic lesions out of 614
2
suspicious lesions), corresponding pooled SS was 81.7% (95%CI: 75.8%-86.7%; I = 37.9%) and pooled SP
was 98.33% (95%CI: 96.5%-99.3%; I = 88.5%) [Figure 8]. Only 7 FP and 38 FN findings were found. Per-
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lung lesion analysis was not performed due to the only 2 articles available.

DISCUSSION
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Our meta-analysis demonstrated the utility of F-FDG PECT/CT in depicting hematogenous metastases
in patients with thyroid cancer. Indeed, the pooled DR for hematogenous metastases was 89.70%.
[32]
Nevertheless, the substantial heterogeneity points out the small samples of the studies .

2
The location of the lesions probably also influenced the heterogeneity (I = 92.84%) of the overall DR, as, in
the subgroup analysis of bone lesions, the variability of DR across the studies was negligible (I = 13.21%).
2
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These data may also indicate a high inter-subject repeatability of F-FDG PECT/CT in depicting lesions
suspicious for bone metastases in patients with thyroid cancer. Although MRI, with the inclusion of DWI,
may assist in the differentiation of cellularity and is generally advocated in the case of vertebral metastases,
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[30]
Sakurai et al. demonstrated a similar DR of MRI compared to F-FDG PECT/CT, whereas Nagamachi
and colleagues documented a lower detectability of lesions by means of MRI in a patient-based analysis
[23]
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compared to F-FDG PECT/CT (84.2% vs. 57.6%) . In our meta-analysis, the three available articles [25,29,30]
documented a SS of 71%, 86%, and 79% and corresponding SP of 100%%, 88%, and 99% for bone lesions
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for F-FDG PECT/CT. Interestingly, Ota et al. proved F-Fluoride PET/CT as a potential optimal
[25]
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alternative to F-FDG PECT/CT for the detection of bone metastases from thyroid cancer, as in their study
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18 F-Fluoride PET/CT demonstrated higher SS and SP compared to F-FDG PECT/CT.