SAN FRANCISCO—Percutaneous image-guided renal mass biopsy (RMB) combined with immunohistochemical (IHC) results can accurately distinguish between benign and malignant tumors, a finding that could help prevent unnecessary nephrectomies, researchers reported at the 37th Annual Scientific Meeting of the Society of Interventional Radiology.

“Traditionally, solid renal masses were not biopsied because if the lesion could not be characterized as benign on imaging, it was presumed to be cancer and was removed surgically,” said study investigator Nisha Alle, BS, who is with the Department of Radiology at David Geffen School of Medicine, University of California-Los Angeles. “But we are finding that a significant subset of these small renal masses is in fact benign on nephrectomy, so it would be helpful to have a pre-procedural biopsy diagnosis of a solid renal mass to avoid any unnecessary surgery or ablation.”

Alle and her colleagues retrospectively studied 173 consecutive patients who underwent percutaneous computed tomography (CT) or ultrasound-guided RMB from March 2002 through January 2012. Biopsies of renal parenchyma for diagnosis of medical renal diseases were excluded. The investigators evaluated imaging variables (including size, location, and extent of disease), number of core biopsies, patient demographics (age, gender), clinical indication, final pathologic diagnosis, IHC studies, and subsequent final pathological diagnosis on nephrectomy. 

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Fourteen of the 173 patients (8.1%) were excluded because biopsies were performed at an outside institution, medical records were incomplete, or lesions were poorly visualized. Three patients had two renal mass biopsies for bilateral renal cell carcinoma (RCC). Of 159 patients with 162 RMB, 114 (71.7%) were male, with a mean age of 69. Of 162 RMB, 111 were malignant (68.5%), 39 were benign (24.1%), and 12 were non-diagnostic (7.4%).

IHC was performed for 110 biopsies (67.9%) and was diagnostic in 93% of those cases; 22 patients underwent subsequent partial nephrectomy. In all cases, RMB was concordant with nephrectomy pathology findings for malignancy. In 76% of cases, RMB was concordant for subtype of RCC. However, in two cases, RMB diagnosis of clear cell RCC was changed to papillary type 2 on nephrectomy. For one patient, RMB diagnosis of papillary type 1 RCC was changed to unclassified RCC, and for another, a biopsy diagnosis of unclassified RCC was changed to clear cell RCC. In another case, an initial diagnosis of unclassified RCC on biopsy was changed to chromophobe. In one case of a non-diagnostic biopsy, the final pathologic diagnosis was solitary fibrous tumor on nephrectomy.

Overall, the combination of RMB and IHC had a sensitivity, specificity, and positive predictive value for detecting malignancy of 100%.

“Routine H&E staining may not able to sufficiently differentiate among different tumor subtypes, but adding immunohistochemical studies for most tumors confers high accuracy for diagnosis,” Alle said. “We only had 12 complications over a time period of 10 years and there were no long-term complications.”

She also noted that no cases of tumor seeding attributed to biopsy were identified.