Evaluation of the morphological features and unfavorable prognostic impact of dirty necrosis in renal cell carcinoma.

PURPOSE Tumor necrosis (TN) is one of the unfavorable prognostic factors in renal cell carcinoma (RCC). We identified two patterns of TN according to their morphology: dirty necrosis and ghost necrosis. We aimed to elucidate the morphological features and unfavorable prognostic impact of dirty necrosis in RCC. METHODS A total of 261 tumors collected after nephrectomy, which were pathologically identified as RCC, were analyzed in this study. We classified TN as dirty necrosis or ghost necrosis and compared their clinicopathological features. We also assessed their morphological features using digitally analyzed slides. The correlation between tumor size and necrosis area or the number of necrotic foci was calculated. RESULTS There were 77 tumors (30%) with TN, and the presence of TN was significantly associated with unfavorable clinicopathological factors. Thirty tumors (39%) had dirty necrosis, and 47 tumors (61%) had ghost necrosis. There were significantly higher numbers of unfavorable factors associated with dirty necrosis than with ghost necrosis. In dirty necrosis, both the TN area and the number of necrotic foci were correlated with tumor size (p < 0.001 and p = 0.003, respectively). However, in ghost necrosis, no correlation was found between tumor size and the number of necrotic foci (p = 0.58). Tumors (without stage IV) with dirty necrosis had a significantly shorter disease-free survival time than those with ghost necrosis and those without TN (p = 0.024 and p < 0.001, respectively). CONCLUSION Dirty necrosis has potential as an unfavorable prognostic indicator of surgically resected RCC.