Squamous cell carcinoma of the palatine tonsils: FDG standardized uptake value ratio as a biomarker to differentiate tonsillar carcinoma from physiologic uptake

Purpose: To quantify fluorine 18 (¹⁸F) fluorodeoxyglucose (FDG) uptake in the palatine tonsils to identify a sensitive and specific metric for distinguishing physiologic asymmetric uptake from squamous cell carcinoma (SCC). Materials and Methods: This HIPAA-compliant retrospective study was approved by institutional review board. Informed consent requirements were waived. Twenty-six patients (seven female, 19 male; mean age, 53.46 years ± 10.45 [standard deviation]) with tonsillar SCC were included. Twenty-six patients (seven female, 19 male; mean age, 61.77 years ± 10.12) with head and neck carcinomas not involving the tonsils were included as control subjects. Tonsil standardized uptake values (SUVs) were measured bilaterally in each group. Independent-samples t test was used to compare mean SUVs, and Pearson correlation was used to evaluate association of FDG uptake between tonsils within control subjects. Results: The mean maximum SUV (SUV_max) of tonsil tumors was 9.36 ± 4.54, which was significantly higher than that of contralateral cancer-free tonsils (2.54 ± 0.88; P < .0001) and tonsils in control subjects (2.98 ± 1.08; P < .0001). In patients with tonsillar cancer, the mean difference in SUV max between tonsils was 10.43 ± 7.07, which was significantly greater than that in control subjects (0.62 ± 0.54; P < .0001). The mean SUV_max ratio between tonsils in patients with carcinoma was 3.79 ± 1.69, which was threefold higher than in control subjects (1.18 ± 0.13; P < .0001). For receiver operating characteristic analysis using SUV_max ratio to differentiate benign uptake from SCC, the area under the curve was 1.00 (95% confidence interval: 1.00, 1.00). A cutoffratio of 1.48 had 100% sensitivity and specificity. Conclusion: The SUV_max ratio represents an accurate imaging biomarker for differentiating tonsillar SCC from physiologic ¹⁸F-FDG uptake.