Immune checkpoint inhibitorsinduced Endocrinopathies on F-18 FDG PET/CT

1350 Background: Immune checkpoint inhibitors (ICI) used in the oncologic practice of advanced hematologic and solid malignancies have reshaped the landscape of treating these illnesses, as they provide a survival benefit. ICI modulate the immune system by augmenting an antitumor lymphocytic response, which can also cause imbalances in immunologic tolerance affecting healthy tissues and manifesting in numerous immune-related adverse events (irAEs). irAEs commonly involve the endocrine system. These complications can be life-threatening and require rapid recognition for proper management, including treatment interruption or systemic glucocorticoids. Understanding the pattern of FDG uptake from ICI-induced endocrinopathies is essential for identifying these AEs and possibly predicting who is at risk for developing AEs. The purpose of this study was to retrospectively identify the PET/CT manifestations of patients with clinically apparent irAEs. Methods: A retrospective review of 435 patients treated with ICI at our institution from 2011 to 2017 was performed. Clinical records were reviewed for demographics, type of cancer, ICI, duration of treatment, biochemical data, and the onset of endocrine irAEs. We reviewed FDG PET/CT scans of patients who received ICI who had a baseline scan at treatment initiation, and a follow-up scan within at least four months of documentation of endocrine irAEs. Results: A total of 55 cases of endocrine adverse events were documented in 54 patients that included thyroid disorders, hypophysitis, adrenal insufficiency, and worsening hyperglycemia. Of the 54 patients, 37 were excluded because they did not have a baseline or follow PET/CT scans. Of the remaining 17 patients, four did not have any abnormalities in endocrine glands and were deemed negative. 13 patients that had adequately performed FDG PET/CT scan were found to have manifestations potentially explained by endocrine irAEs. More than one endocrine gland could be affected in each patient. PET/CT abnormalities included diffuse increased uptake in 12 patients in which 11 was clinically documented. Interval increased in the pituitary gland was found in 5 patients; however, there was no documentation of hypophysitis in those. One patient had increased adrenal uptake with documented adrenal insufficiency. Conclusions: Of the 435 patients that received ICI, 54 (12.4%) patients developed endocrine irAEs. Seventeen patients had adequate PET/CT, and 13 (76.5%) had imaging manifestations that were evident by PET/CT. This preliminary data suggest that whole-body FDG PET/CT can be a useful noninvasive tool for assessing irAEs, including endocrinopathies. Adequate PET/CT acquisition should include the skull base in the field of view so that irAEs involving the pituitary gland are not missed. A baseline scan is necessary to differentiate from physiologic organ uptake from a different benign process and those related to irAEs. Association of irAEs and clinical response to ICI has been noted, and more in this regard should be evaluated not only with metabolic imaging but also with upcoming immune checkpoint expression molecular imaging that could predict treatment response and possible adverse events. More extensive data need to be analyzed to corroborate the above findings further.