Introduction: Most surgically removed benign renal tumors are found to be oncocytic neoplasms including oncocytoma or hybrid oncocytic/chromophobe tumors (O/HOCT). However, these tumors are difficult to differentiate from chromophobe renal cell carcinoma (ChRCC) even with renal mass biopsy as both often exhibit CD117(+) staining. We aimed to validate peak early enhancement ratio (PEER) on preoperative computed tomography compared to surgical pathology to differentiate O/HOCT from ChRCC.
Methods: Patients diagnosed with O/HOCT or ChRCC at nephrectomy were retrospectively identified (2006-2020). Two reviewers blinded to histology by a third party measured enhancement and tumor parameters on preoperative CT imaging. PEER was calculated (net tumor / net cortex) with raters averaged for primary analysis. Correlation between raters was assessed. Clinical factors including age, sex, tumor size, and laterality were assessed. Scatter plots, logistic regression models, and receiver operator curves evaluated the association of PEER and clinical variables to predict final histology. Subanalyses were conducted among CD117(+) confirmed patients
Results: A total of 77 patients were included with 33 (42.9%) O/HOCT and 44 (57.1%) ChRCC. PEER was higher for O/HOCT (median 0.79 (IQR 0.70-0.88) compared to ChRCC (median 0.44 (IQR 0.36-0.55) tumors (p < 0.001). PEER and tumor size were significant predictors of histology (PEER per 0.1 increase (OR 0.32 (95%CI 0.20-0.51), p<0.001), tumor size per 1cm (OR 1.48 (95%CI 1.06-2.07), p=0.02)). Age, sex, laterality, and presence of stellate scar were not significant predictors. AUC for PEER alone was 91.3% and PEER with tumor size increased to 93.0%. A 0.60 cutoff for PEER demonstrated sensitivity and specificity of 87.9% and 90.0%, respectively, to identify O/HOCT. A subset analysis among CD117(+) confirmed patients (N=44) yielded similar values (92.3% sensitivity, 90.3% specificity). Interrater correlation was high (r=0.861).
Conclusions: PEER reliably differentiates benign renal O/HOCT from malignant ChRCC with excellent diagnostic performance. In a diagnostic pathway with renal mass biopsy and CD117 staining, nephrectomy may be avoidable for benign oncocytic neoplasms.
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