Tumor necrosis adds prognostically significant information to grade in clear cell renal cell carcinoma: A study of 842 consecutive cases from a single institution. Khor LY, Dhakal HP, Jia X, Reynolds JP, McKenney JK, Rini BI, Magi-Galluzzi C, Przybycin CG.Am J Surg Pathol. September 2016;40(9):1224-1231

Tumor necrosis has been shown to be an independent predictor of adverse outcome in renal cell carcinoma. A modification of the International Society of Urological Pathology (ISUP) grading system for renal cell carcinomas has recently been proposed, which incorporates the presence of tumor necrosis into grade. The investigators proposing this system found that necrosis added significant prognostic information to ISUP grade. We attempted to describe our experience with the effect of tumor necrosis in relationship to nuclear grade by reviewing the slides from a large consecutive series of localized clear cell renal cell carcinomas from our institution and obtaining long-term clinical follow-up information (overall survival). Of the 842 clear cell renal cell carcinomas reviewed, 265 (31.5%) were ISUP grade 1 or 2, 437 (51.9%) were ISUP grade 3, and 140 (16.6%) were ISUP grade 4. Tumor necrosis was present in 177 (21%) cases. A total of 547 (64.9%) cases were stage pT1, 83 (9.9%) were stage pT2, 193 (22.9%) were stage pT3a, and 19 (2.3%) were pT3b or higher. Median follow-up was 73.2 months (range: 0.12-273.6), and 310 (36.8%) patients died. On univariable analysis, there was no significant difference in outcome for tumors of ISUP grades 1 to 3. After adjustment for age, tumor stage, and tumor size, ISUP grade 4 and necrosis were significant predictors of overall survival on multivariable analysis. When the recently proposed modified grading system incorporating tumor necrosis was applied to our data, there was no significant difference in overall survival between patients with modified grade 1 tumors and those with modified grade 2 tumors (P = 0.31); however, there was a statistically significant difference between patients with modified grade 1 or 2 tumors and those with modified grade 3 tumors (P = 0.04), and a substantial difference in outcome between those with modified grade 3 and modified grade 4 tumors (P0.001). When a recursive partitioning approach was applied to our data, patients of a given ISUP grade could be further prognostically separated according to the presence or absence of necrosis and could be divided into 3 statistically significant prognostic groups: (1) non-necrotic ISUP grade 1 to 3 tumors, (2) ISUP grade 1 to 3 tumors with necrosis and ISUP grade 4 tumors with10% necrosis, and (3) ISUP grade 4 tumors with10% necrosis. In conclusion, our study shows that tumor necrosis adds additional prognostic information to ISUP grade and that quantification of necrosis can further stratify patients with ISUP grade 4 tumors.