PSAT025 Functional Adrenocortical Oncocytic Neoplasm: A Rare Cause of ACTH Independent Cushing's Syndrome

BACKGROUND: Adrenal oncocytomas (AOCs) or adrenocortical oncocytic neoplasms (ACONs) are extremely rare tumors of adrenal glands characterized by the presence of oncocytes, which are epithelial cells with eosinophilic cytoplasm. Only about 140 cases have been reported in literature so far. AOCs are more common in females (2.5: 1), more prevalent on the left adrenal gland (3.5: 1), and tumor size ranges from 3 to 17 cm. About two thirds of AOCs are reported to be nonfunctioning, and only less than 6% of functioning are cortisol secreting. The malignant potential of these tumors has been described quite variably in current literature. Based on the most recent systematic literature review, about 35% were found to be benign, 24% malignant, and 41% borderline, based on the Lin Weiss Bisceglia system. The mainstay of treatment is surgical resection. Here we describe a case where biochemical workup and pathology revealed a functional AOC with uncertain malignant potential. CLINICAL CASE: A 68 year old female with hypertension was found to have an incidental left 3 cm adrenal nodule on CT abdomen and pelvis during a workup for hematuria. The nodule was biopsied and initially found to be benign. Afterwards, she was referred to endocrinology where biochemical testing was consistent with ACTH-independent Cushing's syndrome. She had three elevated late night salivary cortisol - 0.10 mcg/dL, 0.14 mcg/dL, and 0.19 mcg/dL (≤0. 09 mcg/dL), three abnormal 1 mg dexamethasone suppression tests - 16.4 mcg/dL, 15.1 mcg/dL, and 17.1 mcg/dL (<1.8 mcg/dL), two normal 24 hour urinary cortisol - 22.5 and 31.5 mcg/24h (4-50 mcg/24h), and ACTH <5 pg/mL (6-50 pg/mL). She was then referred to surgery and was treated by laparoscopic adrenalectomy. Surgical pathology showed a 3.5 cm adrenal cortical tumor with oncocytes infiltrating into the periadrenal adipose tissue, with positive staining for synaptophysin and negative for P53. On Ki67 staining, some hot spots were greater than 5%. Therefore, the tumor was characterized as AOC with undetermined malignant potential or a low grade, oncocytic adrenocortical carcinoma. She was evaluated by oncology and radiation oncology, and it was decided to monitor the patient without systemic therapy or adjuvant radiation therapy. A surveillance approach was favored given that the risks of adjacent bowel and kidney toxicity outweighed the benefits of radiation. CONCLUSION: We hereby report a case of AOC with undetermined malignant potential. This case highlights many challenges in the diagnosis, management and long-term surveillance of patients with AOCs, and need for further research. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.