Peak early-phase enhancement ratio on contrast-enhanced MRI to differentiate chromophobe renal cell carcinoma from oncocytoma

Objectives: To evaluate the feasibility of using the peak early-phase enhancement ratio (PEER) of tumour to renal cortex measured on contrast-enhanced magnetic resonance imaging (MRI) to distinguish between chromophobe renal cell carcinoma (chRCC) and oncocytoma, which are difficult to differentiate on renal mass biopsy. Patients and Methods: A consecutive case–control study was conducted of patients with chRCC or oncocytoma based on surgical pathology (2006–2020). Two radiologists blinded to pathology results independently measured PEER values on MRI for each tumour. PEER values were compared with surgical pathology results. Results: For the 18 renal tumours evaluated, PEER values were higher for the 7 oncocytomas than for the 11 chRCCs (median 1.33 versus 0.55, p < 0.001). Agreement between the image interpreters was high (Pearson's: 0.90). PEER cutoff values ranging from 0.98 to 1.05 provided high performance in identifying chRCC. A PEER cutoff value of ≤1.05 had sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of 100% for the averaged PEER measurements between the two radiologists. High accuracy in identifying chRCC was also achieved for each individual image interpreter using the cutoff value of ≤1.05, with sensitivity of 100%, specificity of 85.7%, PPV of 91.7% and NPV of 100% for radiologist #1 and sensitivity of 90.9%, specificity of 85.7%, PPV of 90.9% and NPV of 85.7% for radiologist #2. Conclusion: Differentiating chRCCs from oncocytomas using PEER measurements obtained from contrast-enhanced MRI is feasible and reproducible between radiologists. We identified an accurate range for PEER cutoff values (0.98 to 1.05) requiring validation and adjustment in additional cohorts to maintain high sensitivity for detecting chRCC and negative predictive value. Using MRI PEER to evaluate oncocytic tumours with a differential diagnosis of chRCC versus oncocytoma based on biopsy pathology may help avoid unnecessary intervention for oncocytomas.