ODP049 Oncocytic adrenocortical carcinoma misdiagnosed as renal oncocytoma and use of urinary steroid profiling in disease monitoring after mitotane therapy

INTRODUCTION: Oncocytic adrenocortical carcinoma (OAC) is a rare, more indolent variant of adrenocortical carcinoma (ACC). With fewer than 70 cases reported in the English literature, the biological behavior and its response to treatment are poorly characterized. The distinction of OAC from other oncocytic neoplasms (e. g., kidneys) and variants of renal cell carcinoma (RCC) may pose diagnostic challenge pathologically. Urine steroid profiling (USP) of OAC has not been previously reported. CASE DESCRIPTION: A 65-year-old Chinese man was incidentally found to have a large left upper abdominal mass in September 2014. A CT urogram showed a 15×13×13cm solid mass in the upper pole of left kidney. Left radical nephrectomy and splenectomy was performed. Pathological examination of the 'nephrectomy' showed oncocytoma. He was managed as having a renal oncocytoma with complete resection with yearly follow-up. In December 2018, a surveillance chest X-ray showed multiple lung nodules over right lung base. PET-CT in June 2019 showed bilateral hypermetabolic lung nodules suggestive of lung metastases. CT guided fine needle aspiration biopsy of lung nodule showed oncocytoma. Pathology review of both the lung and 'nephrectomy' biopsy revealed identical cores of oncocytic tumor cells while immunohistochemical studies displayed positivity for SF-1 and Melan-A suggestive of adrenocortical origin. In the presence of lung metastases, a revised diagnosis of OAC was made with the original tumor classified as oncocytic adrenocortical neoplasm of uncertain malignant potential by the Lin-Weiss-Bisceglia system. Hormonally the tumor was non-functional with suppressible cortisol post 1mg overnight dexamethasone suppression test and normal renin, aldosterone, estradiol and DHEA-S levels. Twenty-four-hour urine steroid profiling showed elevated tetrahydro-11-deoxycortisol 788ug/day [RR 10-90µg /day], pregnanediol 374µg /day [RR 41-348µg/day] and pregnenetriol 487µg /day [RR 25-256µg /day]. Mitotane was started and titrated up to 1500mg daily, aiming at a serum mitotane level of 14- 20µg /ml. Resolution of lung metastases was noted 6 months later and the abnormal urinary steroid metabolites were also normalized. The patient remained in disease remission 18 months after commencement of mitotane. CONCLUSION: Oncocytic adrenocortical carinoma may be mistaken as other oncocytic neoplasms or variants of RCC pathologically and is classified by the Lin-Weiss-Bisceglia system. An accurate diagnosis has significant impact on disease prognostication and management. OAC may respond more favorably to mitotane monotherapy in comparison to typical ACC. Urine steroid profiling is potentially useful in the surveillance and disease monitoring of OAC. Reference: (1) Harada et al. A rare case of oncocytic adrenocortical carcinoma clinically presented as an incidentaloma. Endocr J. 2020 Aug 28;67(8): 883-888. Presentation: No date and time listed