ODP020 A Challenging Case of Poorly Differentiated Carcinoma with Neuroendocrine Differentiation and Adrenal Mass

BACKGROUND: Neuroendocrine tumors (NETs) account for about 0.5% of all newly diagnosed malignancies. The most frequent primary sites are the gastrointestinal tract or pancreatic (62%-67%) and the lung (22%-27%). All poorly differentiated NETs have a Ki-67 index of greater than 20% and WHO grade of 3. The determination of the site of origin can be challenging in widely metastatic poorly differentiated NETs. CLINICAL CASE: A 51-year man with a history of hypertension and type 2 diabetes mellitus presented with angioedema while on lisinopril for years. Apart from a month's history of bilateral flank pain, he denied diarrhea, flushing, stridor, or shortness of breath. CT abdomen showed an 8.2×8. 0×7.9 cm right adrenal mass with a few punctate calcifications, hepatomegaly with multiple liver metastases, multiple retroperitoneal, hepatoduodenal, retrocrural adenopathy, and T4 metastatic lesion. CT chest showed bulky mediastinal and supraclavicular lymph nodes with trachea narrowing. All those lesions were FDG avid on PET/CT scan. Core biopsy of right supraclavicular lymph node revealed a poorly differentiated carcinoma with neuroendocrine differentiation and high proliferative index (25-50%). On cell block, it was negative for (AE1/AE3 (-), CAM5.2 (-), CK7, CK20, vimentin, desmin, CEA, EMA, CD45, CD20, and TTF-1 but positive for CK903 (focal +), synaptophysin (+), chromogranin (+), calretinin (focally +), inhibin (focally +). Based on the immunohistochemical stain, it was concluded as a metastatic small cell carcinoma of unknown origin. He was treated with carboplatin, etoposide, and atezolizumab and received 5 cycles. Endocrine was consulted two months after his initial presentation. Urine normetanephrine was > 4-fold elevated. Blood pressure was controlled on Doxazosin at 4 mg bid. The 10 gene-panel for hereditary pheochromocytoma and Paraganglioma (PGL) was negative. There was a progression of mediastinal adenopathy while on treatment with narrowing of proximal intrathoracic trachea requiring elective tracheostomy. Based on imaging findings and elevated normetanephrine, we believe he has metastatic pheochromocytoma and PGL. His chemo regimen was switched to Cyclophosphamide, Vincristine, and Dacarbazine (CVD). He finished 8 cycles of CVD with an overall reduction in the size of lymph nodes (both above and below the diaphragm) and right adrenal mass. His plasma normetanephrine level was also significantly improved. Presentation: No date and time listed