Prevalence and significance of incidental findings on 68 Ga-DOTA-conjugated somatostatin receptor-targeting peptide PET/CT: a systematic review of the literature

AIM: We aimed to evaluate the prevalence of incidental 68 Ga-DOTA-conjugated somatostatin receptor-targeting peptide PET/CT (SSTR PET/CT) findings, their clinical significance in the need for follow-up, and their risk of malignancy.

MATERIALS AND METHODS: Studies reporting incidental SSTR PET/CT findings were systematically searched in PubMed, Cochrane, Embase and Web of Science literature published prior to 1st of May 2020. Studies were filtered by two independent readers for eligibility based on title and abstract, and subsequently on full text. The main exclusion criteria were: 1) pathological findings that matched scan indication, 2) known organ specific disease and/or incidental findings confirmed on other scan modality prior to SSTR PET/CT, 3) lack of diagnosis and/or follow up, and 4) results published in proceedings or conference abstracts.

RESULTS: Twenty-one studies, comprising a total of 2906 subjects, were eligible for the analysis. Studies included were retrospective cohort studies on incidental SSTR PET/CT findings in a specific organ (n = 2888, 7/21) or case reports (n = 18, 14/21). A total of 133 subjects had incidental SSTR PET/CT findings. Incidental findings were predominantly seen in the thyroid gland (n = 65), spine (n = 30), brain (n = 26) and breast (n = 6). Seventeen of 133 (13%) incidental findings were malignant on final diagnosis. Incidental breast findings were associated with the highest risk of malignancy (67%). In the thyroid, incidental SSTR uptake was caused by malignancy in 8%, all presenting as focal uptake. The lowest risk was seen in the spine with a malignancy rate of 3% in patients with incidental SSTR uptake and benign cases were interpreted as vertebral hemangiomas on CT. Incidental SSTR PET/CT findings in other locations were of malignant etiology in two out of six cases (33%) and should be evaluated individually.

CONCLUSION: The most incidental SSTR PET/CT findings were found in the thyroid gland, spine, and brain. The risk of malignancy was greatest in incidental SSTR PET/CT findings in the breast, cranially, and thyroid gland. The results of the present study can prove useful in the interpretation of atypical findings on SSTR PET/CT and in the counseling of clinicians.