Depth of mesorectal extension has prognostic significance in patients with T3 rectal cancer.

Background: More than half of all rectal cancers are T3 lesions, but they are classified as a single-stage category.

Objective: The aim of this study was to validate prognostic significance of mesorectal extension depth in T3 rectal cancer.

Design: This study is a retrospective analysis of oncologic outcomes of patients with T3 rectal cancer grouped by mesorectal extension depth (T3a, <1 mm; T3b, 1-5 mm; T3c, 5-15 mm; T3d, >15 mm).

Settings: This study was conducted at a tertiary referral cancer hospital.

Patients: From 2003 to 2009, 291 patients who underwent a curative surgery were included.

Main Outcome Measures: Oncologic outcomes in terms of disease-free survival were analyzed.

Results: The 5-year disease-free survival rate according to T3 subclassification was 86.5% for T3a, 74.2% for T3b, 58.3% for T3c, and 29.0% for T3d. It was significantly higher in T3a,b tumors than that in T3c,d tumors (77.6% vs 55.2%, p < 0.001). On univariate and multivariate analysis, prognostic factors affecting recurrence were preoperative CEA level ≥ 5 ng/mL (HR 2.617, 95% CI 1.620-4.226), lymph node metastasis (HR 3.347, 95% CI 1.834-6.566), and mesorectal extension depth >5 mm (HR 1.661, 95% CI 1.013-2.725). In subgroup analysis, independent prognostic factors were preoperative CEA level and mesorectal extension depth >5 mm for 200 patients with ypT3 rectal cancer and preoperative CEA level and lymph node metastasis for 91 patients with pT3 rectal cancer.

Limitations: This study lacks quality of surgery plane evaluation because of its retrospective nature. Moreover, pathologic examination was not done with a whole-mount section.

Conclusions: Depth of mesorectal extension >5 mm is a significant prognostic factor in patients with T3 rectal cancer. Depth of mesorectal extension especially may be more important than the nodal status in predicting the oncologic outcome for patients who had received preoperative chemoradiotherapy.