Predicting oncologic outcomes by stratifying mesorectal extension in patients with pT3 rectal cancer: a Japanese multi-institutional study.

The goal of this study was to clarify the clinical significance of mesorectal extension in pT3 rectal cancer. This currently remains unclear. Data from 975 consecutive patients with pT3 rectal cancer that underwent curative surgery at 28 institutes were reviewed. The distance of the mesorectal extension (DME) was measured histologically. The optimal prognostic cut-off point of the DME for oncologic outcomes was determined using the receiver operating characteristic curve and Cox regression analysis. When patients were subdivided into two groups according to the optimal cut-off point, DME≤4 mm and DME>4 mm, DME was found to be a powerful independent risk factor for postoperative recurrence. A DME>4 mm was significantly correlated with distant and local recurrences at Stage IIA and IIIB diseases. The recurrence-free 5-year-survival rate was significantly higher in patients with a DME≤4 mm [86.6% at Stage IIA (p=0.00015), and 68.7% at Stage IIIB (p<0.0001)] than in patients with a DME>4 mm (71.3% at Stage IIA and 49.1% at Stage IIIB). No significant difference was noted in the oncologic outcomes between the two groups at Stage IIIC. A value of 4 mm provides the best prognostic cut-off point for patient stratification and for the prediction of oncologic outcomes. A subclassification based on a 4-mm cut-off point may improve the utility of the TNM 7th staging system except for Stage IIIC. These findings warrant further prospective studies to determine the reliability and validity of this cut-off point.