(UroToday.com) At the Society of Urologic Oncology (SUO) Annual Virtual Meeting, Dr. Brian Shuch reviewed strategies for identifying renal masses as oncocytoma, a type of benign renal mass. Although not as common as renal cell carcinoma (RCC), oncocytomas are not uncommon and account for 3-5% of renal masses and approximately 25% of small renal masses.
Oncocytomas present as a solid, enhancing renal masses on cross-sectional imaging and are often indistinguishable from a renal cell carcinoma on conventional imaging, prompting Dr. Shuch to describe oncocytoma as the “RCC Doppelganger”. But unlike RCC which may grow and become locally destructive or has the ability to develop metastatic spread if left untreated, oncocytomas rarely cause local symptoms or pain and do not have the ability to develop metastatic spread. As a result, most oncocytomas can safely be surveilled and do not need to be treated, suggesting patients have little to gain from the treatment of oncocytoma but still incur the risks of surgery – such as pain, DVT/PE, hernia, or even death – when treated.
Dr. Shuch explains the limitations of renal mass biopsy to identify which lesions are oncocytomas. Renal mass biopsies are seldom utilized, reporting only 10% of patients with small renal masses to undergo a biopsy. Additionally, biopsy specimens of oncocytoma can look similar to chromophobe RCC when examined microscopically. Pathologists are often timid to definitely call a renal mass an oncocytoma from a biopsy specimen, leading to the quandary of a non-diagnostic biopsy and the need for new methods to identify which renal masses are oncocytomas and which are RCC.
Dr. Shuch presents data pioneered from the Johns Hopkins group utilizing 99mTc-sestamibi SPECT/CT scans to differentiate oncocytoma from RCC without a biopsy1. The 99mTC-sestamibi tracer, which is typically used in patients with hyperparathyroidism to aid in identifying the hypersecreting parathyroid gland, localizes to mitochondria within cells. Microscopically oncocytomas are rich in mitochondria. As a result, renal masses that are oncocytoma will strongly take up the 99mTc-sestamibi tracer while renal masses that are RCC will not take up the tracer, making 99mTc-sestamibi an attractive, noninvasive method to differentiate oncocytomas from RCC.
Additionally, Dr. Shuch presented several molecular methods identifying oncocytomas, including his own research establishing a transcriptome signature of oncocytomas. Dr. Shuch identified nine genes differentially expressed in oncocytoma compared with chromophobe RCC2. The Oncocytic Gene Expression (or ONEX) classifier demonstrates impressive accuracy in identifying oncocytoma from chromophobe RCC, with a sensitivity of 93%, the specificity of 98%, and c-statistic of 0.98.Dr. Shuch presents promising results from several modalities to aid in the differentiation between oncocytoma and RCC. One question left unanswered is how the relative rarity of oncocytoma compared with RCC may affect scalability and widespread use of these technologies, as many patients will have to be tested in order to identify the few oncocytomas among many RCCs.
With future work refining these methods, Dr. Shuch hopes we can accurately identify renal masses that are oncocytoma, thereby avoiding or limiting the overtreatment and morbidity from treatment in patients with these benign renal masses.
Presented by: Dr. Brain Shuch, MD, Director of the Kidney Cancer Program and the 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, during the 21st Annual Meeting of the Society of Urologic Oncology (SUO), December 3-5, Virtual Conference
References
1. Gorin, M. A., Rowe, S. P., Baras, A. S. et al.: Prospective Evaluation of (99m)Tc-sestamibi SPECT/CT for the Diagnosis of Renal Oncocytomas and Hybrid Oncocytic/Chromophobe Tumors. Eur Urol, 69:413, 2016
2. McGillivray, P. D., Ueno, D., Pooli, A. et al.: Distinguishing Benign Renal Tumors with an Oncocytic Gene Expression (ONEX) Classifier. Eur Urol, 2020