SUN-904 Ga68 Dotatate Detects Ectopic ACTH Secreting Atypical Carcinoid Tumor

Abstract

Title Ga68 DOTATATE detects Ectopic ACTH secreting Atypical Carcinoid tumor Introduction Ga-68 DOTATATE PET/CT has been shown to have a significant impact in localizing Ectopic ACTH secreting tumors especially those that are not identified on conventional imaging (CT, MRI). We present a person with a tumor that was reported benign (on biopsy) elsewhere but was found to be the source of the Cushings syndrome and was localized on Ga-68 DOTATATE PET/CT, pathology confirming atypical carcinoid tumor after surgical excision. Discussion She was a 63-year-old who presented with a severe proximal myopathy, high urinary free cortisol- 911.6 (µg/day) (<45), elevated ACTH 104(<63), and negative Inferior Petrosal Sinus Sampling. The CT scan demonstrated a small nodule at the right lung base. Axial Ga-68 DOTATATE PET images demonstrated radiotracer activity in the lesion, SUV max of 7.15. Fused Coronal Images showed a 1.9 cm radiotracer avid nodule, that was detected in the medial segment of the right middle lobe. The patient underwent a pulmonary wedge resection. H and E stain of the tumor -Immunohistochemical stains demonstrated that the tumor was strongly positive for synaptophysin and INSM-1 (markers of neuroendocrine differentiation) and the mitotic count was up to 2–3 mitoses per 10 high-power fields, supporting diagnosis as an atypical carcinoid tumor. The patient had significant improvement of symptoms post excision. Somatostatin Receptor (SSR) based tracer Ga-68 DOTATATE PET/CT has a reported sensitivity for detection of 50 % in occult neuroendocrine tumors (NET), with an overall sensitivity of 64 % in a systematic review. It has been shown in retrospective reviews to help with clinical management both at initial diagnosis as well as follow up of Ectopic Cushings in approximately 65% of the cases. SSR analogue tracers like DOTATATE have been noted to be slightly better than FDG PET/CT at localizing ACTH producing bronchial carcinoids while small-cell lung cancers and other aggressive tumors are better visualized on FDG PET. The favorable aspect of Ga-68 DOTATATE includes great tumor to background ratio and the half-life of Gallium 68 that is suitable for transport and delivery. Metastatic NET in conjunction with ectopic Cushing syndrome can be also be treated with peptide receptor radionuclide therapy using either 90Y-DOTATOC and 177Lu-DOTATATE (both SSR based) resulting in improved clinical outcomes.