Tool differentiates renal oncocytoma, chromophobe RCC

A simple radiographic measurement has been identified and prospectively evaluated that can differentiate CD117-positive renal oncocytomas (ROs) from CD117-positive chromophobe renal cell carcinomas (RCCs) with apparent 100% accuracy, investigators said.

The tumor:cortex peak early-phase enhancement ratio (PEER), obtained using standard multiphase computed tomography (CT), correctly classified 41 out of 41 CD117-positive cases as ROs or chromophobe RCCs, they reported in Clinical Cancer Research (2018; 24:3898-907).

The finding suggests that, in the setting of a CD117-positive renal tumor biopsy, this modality could substantially reduce patient morbidity and health care costs by avoiding the need for resection in benign cases, said Eric C. Kauffman, MD, of Roswell Park Cancer Institute, Buffalo, NY.

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However, given this limited experience to date in just 41 cases, more research is needed to confirm the clinical value of a high PEER value for diagnosis of CD117-positive ROs, Dr. Kauffman said in an interview with Urology Times.

“We need larger numbers, and more importantly, we need external validation from other institutes,” he said.

Dr. Kauffman and colleagues first identified PEER as a potential clinical variable that could improve preoperative differentiation of renal tumor biopsies in a retrospective analysis of 93 RO or chromophobe RCC tumors that were resected between 2003 and 2012.

They found some clinical variables, including tumor size and age, were associated with chromophobe RCC.

However, the most reliable variable turned out to be the CT peak signal intensity in a tumor, especially when expressed as a ratio of tumor to cortex. The authors further observed that differences in tumor:cortex signal intensity between RO and chromophobe RCC were greatest when using an early contrast phase, as opposed to a delayed phase.

Continue to the next page for more.All of the RO tumors were relatively hyperenhancing with a tumor:cortex PEER of 0.50 or greater, according to their report. Conversely, the chromophobe RCCs were relatively hypoenhancing, at a PEER of 0.50 or less-except for four cases with a PEER over 0.50, all of which turned out to be CD117-negative, investigators found.

Subsequently, Dr. Kauffman and co-investigators looked at PEER prospectively in 22 additional tumors that were specifically CD117-positive, and the CT enhancement measure once again correctly classified all of them as RO or chromophobe RCC.

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The prospective inter-observer reproducibility was excellent for peer scoring, with an intra-class correlation coefficient of 0.97, and perfect for assignment of RO versus chromophobe RCC, at 1.0, according to Dr. Kauffman and colleagues.

“It was very encouraging that this tool showed a very high reproducibility among our own different observers,” Dr. Kauffman said. “They had different levels of radiologic expertise, and despite that, their independent scoring of every tumor was remarkably similar.”

Dr. Kauffman and co-authors had no conflicts of interest to report related to this study, which was supported in part by a grant from the National Cancer Institute.