Quantification of sarcomatoid differentiation in renal cell carcinoma on magnetic resonance imaging

Sarcomatoid differentiation in renal cell carcinoma (sRCC) is histologically characterized by anaplastic changes of renal cell carcinoma (RCC) subtypes, which has been associated with a poor prognosis. sRCC is managed more aggressively than RCC without sarcomatoid components, so pre-operative detection of sarcomatoid differentiation would significantly affect surgical management. The purpose of this study is to compare the quantification of sarcomatoid features in RCCs on pre-operative magnetic resonance imaging (MRI) to standard histological examination.

Patients who had nephrectomy at our institution between 2000 and 2015 with pathology proven RCC and pre-operative contrast enhanced MRI abdominal scans were retrospectively reviewed. A custom MATLAB routine calculated the portion of each manually segmented whole tumor with MRI signal suggestive of sarcomatoid involvement based on prior research (MRI%SARC). The primary endpoint compared MRI%SARC to percent sarcomatoid involvement estimated by histological examination (HIST%SARC) using Pearson correlation and Bland Altman analysis.

A total of 17 patients with sRCC (10 males, age 60.3±11.1 years) and 17 consecutive control patients with clear cell RCC (ccRCC) without sarcomatoid components (10 males, age 64.5±7.6 years) were evaluated. Pearson correlation analysis revealed a strong association between MRI%SARC and HIST%SARC (r=0.782, P<0.001). Bland-Altman analysis demonstrated proportional bias, with a mean bias of 19.29 [95% confidence interval (CI): 9.79-28.79] and with 95% limits of agreement of -16.93 (95% CI: -33.38 to -0.48) to 55.51 (95% CI: 39.06-71.96), suggesting MRI%SARC underestimated values compared to HIST%SARC by 19%.

Multiparametric pre-operative MRI analysis to quantify sarcomatoid features in RCC correlates with standard histological examination but underestimates percent sarcomatoid involvement.