(UroToday.com) At the Society of Urologic Oncology (SUO) annual virtual meeting, Dr. Brian Shuch examined strategies for identifying kidney masses as oncocytoma, a type of benign kidney mass. Although not as common as renal cell carcinoma (RCC), oncocytomas are not uncommon and account for 3-5% of kidney masses and approximately 25% of small kidney masses.
Oncocytomas present as solid, increasing renal masses on cross-sectional imaging and are often indistinguishable from renal cell carcinoma on conventional imaging, prompting Dr. Shuch to describe the oncocytoma as “RCC Doppelganger”. But unlike RCC which can grow and become locally destructive or has the ability to develop metastatic spread if left untreated, oncocytomas rarely cause local symptoms or pain and lack the ability to develop metastatic spread. As a result, most oncocytomas can be safely supervised and should not be treated, suggesting that patients have little to gain from oncocytoma treatment but still run the risks of surgery – such as pain, DVT / PE, hernia or even death – when treated.
Dr. Shuch explains the limitations of kidney mass biopsy to identify which lesions are oncocytomas. Renal mass biopsies are rarely used, signaling that only 10% of patients with small renal masses need biopsy. Additionally, oncocytoma biopsy specimens may appear similar to chromophobic RCC when examined under a microscope. Pathologists are often shy about definitively calling a kidney mass an oncocytoma from a biopsy sample, leading to the dilemma of a non-diagnostic biopsy and the need for new methods to identify which kidney masses are oncocytomas and which are RCCs.
Dr. Shuch presents data pioneered by the Johns Hopkins group using SPECT / CT 99mTc-sestamibi scans to differentiate oncocytoma from RCC without a biopsy1. The 99mTC-sestamibi tracer, which is typically used in patients with hyperparathyroidism to aid in the identification of the hypersecretory parathyroid gland, is located in the mitochondria within cells. Microscopic oncocytomas are rich in mitochondria. Consequently, renal masses that are oncocytoma will strongly absorb the 99mTc-sestamibi tracer while renal masses that are RCC will not absorb the tracer, making 99mTc-sestamibi an attractive and non-invasive method of differentiating oncocytomas from RCC.
Additionally, Dr. Shuch presented several molecular methods for identifying oncocytomas, including his research establishing a transcriptome signature of oncocytomas. Dr. Shuch identified nine differentially expressed genes in oncocytoma versus chromophobic RCC2. The Oncocytic Gene Expression (or ONEX) classifier demonstrates incredible accuracy in identifying chromophobic RCC oncocytoma, with a sensitivity of 93%, a specificity of 98%, and a c-statistic of 0.98.
Dr. Shuch presents promising results from several modalities to aid in the differentiation between oncocytoma and RCC. An unanswered question is how the relative rarity of oncocytoma compared to RCC may affect the scalability and widespread use of these technologies, as many patients will need to be tested to identify the few oncocytomas among many RCCs.
With future work refining these methods, Dr. Shuch hopes we can accurately identify kidney masses that are oncocytoma, thereby avoiding or limiting overtreatment and morbidity from treatment in patients with these benign kidney masses.
Presented by: Dr. Brain Shuch, MD, Director of the Kidney Cancer Program and Alvin & Carrie Meinhardt Endowed Chair in Kidney Cancer Research, University of California Los Angeles, California, United States.
Written by: Kevin Ginsburg, MD, and Adrien Bernstein, MD, Society of Urologic Oncology Fellow, Fox Chase Cancer Center, Fox Chase Cancer Center, Philadelphia, PA, at the Society of Urologic Oncology (SUO) 21st Annual Meeting, December 3-5, Virtual conference
1. Gorin, MA, Rowe, SP, Baras, AS et al.: Prospective evaluation of (99m) Tc-sestamibi SPECT / CT for the diagnosis of renal oncocytomas and hybrid oncocytic / chromophobic tumors. Eur Urol, 69:413, 2016
2. McGillivray, PD, Ueno, D., Pooli, A. et al .: Distinguish benign renal tumors with an oncocytic gene expression classifier (ONEX). Eur Urol, 2020