Great difference in survival may be solved by Dukes C patients subclassification related to positive nodes number. 
Chemical lymph nodes clearance is a superior technique to identify the total number and the positive lymph nodes in 
colorectal cancer surgery. In the present study we investigated the clinico-pathological association of positive lymph node numbers, level, with their number in every level and their prognostic value. Also, the effect of mesentry level ligation on patient's survival was considered. 
This study was conducted on 54 patient of Dukes C colorectal adenocarcinoma, who were subjected to colectomy radical 
operations. Xylene chemical clearance was applied to resected specimens for lymph node dissection. The lymph nodes were identified in three levels, pericoloic within 5 cm. of tumor edge, paracolic within 5-10 cm of tumor edge and those along the main blood vessels. The patients were followed for minimum period of two years. 
The mean number of examined nodes per specimen was 21.03 (range, 5-39) while, the mean number of positive nodes was 3.09 (range, 1-14). There was a significant correlation between young age and higher number of positive nodes and perineural invasion. Also, significant correlation was identified between nodes level and higher grade as well as perineural invasion. The 2 years disease free survival (2DFS) was significant with nodes level but not the number. On the other hand, the 2 years disease free time (2DFT) was significant with nodes number, level, and the number within every level. 
The tumor grade, positive lymph nodes within every level as detected by chemical clearance should be considered in 
accurate assessment of prognosis after colectomy.