Extent of mesorectal tumor invasion as a prognostic factor after curative surgery for T3 rectal cancer patients.

Abstract

To determine the significance of the extent of mesorectal tumor invasion as a prognostic factor for T3 rectal cancer patients. There is controversy as to which primary lesion characteristics, other than regional lymph node involvement, in T3 rectal cancer are reliable prognostic factors. The extent of mesorectal tumor invasion was evaluated using 2 data sets comprising 196 and 247 patients undergoing curative surgery at separate institutes. When the outer aspect of the muscular layer was not identifiable, an estimate was obtained by drawing a straight line between the 2 break points of the muscular layer. We selected 6 mm as the optimal value for subclassification of T3 rectal patients into 2 groups, based on the extent of mesorectal invasion, using the first data set. The overall 5-year survival rate was significantly higher in patients with <6 mm than in those with > or =6 mm of mesorectal invasion (72% versus 50%; P< 0.01). Similarly, in the second data set, the overall 5-year survival rates of patients with mesorectal invasion <6 mm and > or =6 mm were 59% and 37%, respectively (P < 0.01). In both data sets, multivariate analyses verified the extent of mesorectal invasion to be an independent prognostic factor, together with nodal involvement. Regarding positive nodal involvement and mesorectal invasion > or =6 mm as risk factors, the overall 5-year survival rates with none, one, and both of these factors were 84%, 61%, and 38%, respectively, in the first data set (P < 0.01). Prognostic results were similar for the second data set. Extent of mesorectal invasion, based on a 6-mm cutoff value, is useful for subclassification of T3 rectal cancer patients.