Renal cell carcinoma: a nomogram for the CT imaging-inclusive prediction of indolent, non-clear cell renal cortical tumours

Aim To develop a nomogram from clinical and computed tomography (CT) data for pre-treatment identification of indolent renal cortical tumours. Patients and methods A total of 1201 consecutive patients underwent dedicated contrast-enhanced CT prior to nephrectomy for a renal cortical tumour between January 2000 and July 2011. Two radiologists evaluated all tumours on CT for size, necrosis, calcification, contour, renal vein invasion, collecting system invasion, contact with renal sinus fat, multicystic tumour architecture, nodular enhancement, and the degree of nephrographic phase enhancement. CT and clinical predictors (gender, body mass index [BMI], age) were incorporated into the nomogram. We employed multivariable logistic regression analysis to predict tumour type and internally validated the final model using the data from reader 1. External validation was performed by using all data from reader 2. We applied Wilcoxon rank sum test and Fisher's exact test to investigate for differences in tumour size, BMI, age, and differences in CT imaging features between patients with aggressive and those with indolent tumours. Results 63.6% (764/1201) of patients had clear-cell or other aggressive non-clear-cell RCC (i.e. papillary RCC type 2, unclassified RCC) and 36.4% (437/1201) had indolent renal cortical tumours (i.e. papillary RCC type 1, chromophobe RCC, angiomyolipoma, or oncocytoma). On CT, indolent tumours were significantly smaller (p < 0.001) than aggressive tumours and significantly associated with well-defined tumour contours (p < 0.001). Aggressive RCC were significantly associated with necrosis, calcification, renal vein invasion, collecting system invasion, contact with renal sinus fat, multicystic tumour architecture, and nodular enhancement (all, p < 0.001). The nomogram's concordance index (C-index) was 0.823 after internal and 0.829 after external validation. Concluding statement We present a nomogram based on 1201 patients combining CT features with clinical data for the prediction of indolent renal cortical tumours. When externally validated, this nomogram resulted in a C-index of 0.829.