Oncocytic Adrenal Neoplasms: Clinical Profiles and Long-Term Outcomes

<b>Background:</b> Oncocytic adrenal neoplasms, defined by ≥90 % of oncocytic cells, are rare. The significance of oncocytic changes within an adrenal neoplasm remains unclear.<b>Methods:</b> A retrospective study of adults who underwent adrenalectomy at a large center identified pure oncocytic neoplasms on final pathology (1997-2022). Neoplasms were categorized based on Lin-Weiss-Bisceglia system as malignant, benign, or of uncertain malignant potential. Analysis was performed using Fisher exact, Kruskal-Wallis tests, and Kaplan-Meier analysis.<b>Results:</b> Among a total of 33 patients, 24% had benign, 36% malignant, and 39% neoplasm of uncertain malignant potential. None of the benign neoplasms recurred, while 50% of the malignant neoplasms recurred (median of 40 months). Two of 13 neoplasms initially thought to be of uncertain malignant potential recurred as distant metastatic adrenocortical carcinoma at 11 and 25 months, over a median follow-up duration of 31 months. Ki67% was available for 20 patients: median (IQR) Ki67% was 5 (1, 5) for benign, 10 (6, 15) for malignant, and 6.5 (5, 10) for neoplasms of uncertain behavior, <i>P</i> = 0.05. Recurred neoplasms had higher Ki67% at initial resection compared to cases that did not recur.<b>Conclusion:</b> While oncocytic adrenal neoplasms are rare, a significant proportion are malignant or have malignant potential. Judicious follow-up is required for oncocytic adrenal neoplasms of uncertain malignant potential, as they can recur as metastatic adrenocortical carcinoma. Ki67% should always be obtained in cases of malignancy or uncertain malignant potential as it can predict recurrence. Larger studies are needed to evaluate the appropriate follow-up protocols for these neoplasms.