F-18-FDG PET/CT Can Predict Development of Thyroiditis Due to Immunotherapy for Lung Cancer

Our primary purpose was to determine whether increased F-18-FDG uptake in the thyroid gland predicts development of thyroiditis with subsequent hypothyroidism in patients undergoing immunotherapy with nivolumab for lung cancer. Secondarily, we determined whether F-18-FDG uptake in the thyroid gland correlates with number of administered cycles of nivolumab. Methods: Retrospective chart review over 2 y found 18 lung cancer patients treated with nivolumab who underwent F-18-FDG PET/CT before and during therapy. SUVmean, SUVmax, and total lesion glycolysis of the thyroid gland were measured. SUVs were also measured for the pituitary gland, liver, and spleen. Patients underwent monthly thyroid testing. PET/CT parameters were analyzed by unpaired t testing for differences between 2 groups (patients who developed hypothyroidism and those who did not). Correlation between development of thyroiditis and number of cycles of nivolumab was also tested. Results: Six of 18 patients developed hypothyroidism. The t test comparing the 2 groups demonstrated significant differences in SUVmean (P = 0.04), SUVmax (P = 0.04), and total lesion glycolysis (P = 0.02) of the thyroid gland. Two of 4 patients who developed thyroiditis and had increased F-18-FDG uptake in the thyroid gland had a normal TSH level at the time of follow-up F-18-FDG PET/CT. Patients who developed thyroiditis with subsequent hypothyroidism stayed longer on therapy (10.6 cycles) than patients without thyroiditis (7.6 cycles), but the trend was not statistically significant. No significant difference in PET/CT parameters was observed for pituitary gland, liver, or spleen. Conclusion: F-18-FDG PET/CT can predict the development of thyroiditis with subsequent hypothyroidism before laboratory testing. Further study is required to confirm the positive trend between thyroiditis and duration of therapy.