Clinical Significance of Subclassification of Lower pT3 Rectal Cancer by the Depth of Tumor Invasion Beyond the Outer Border of the Muscularis Propria

Masayoshi Miyoshi, Yojiro Hashiguchi, Hideki Ueno, Hajime Fujimoto and Hidetaka Mochizuki

The First Department of Surgery, National Defense Medical College

Purpose: We measured the distance of tumor invasion beyond the outer border of the muscularis propria (mp) and analyzed whether it would be useful prognostic factor of lower pT3 rectal cancer (RC) patients. Methods: Between 1977 and 1997, 196 patients with pT3 lower RC underwent potentially curative operation. The depth of tumor invasion beyond the outer border of mp (depth beyond mp) was measured. Risk factors for survival after surgery such as depth beyond mp, tumor size, macroscopic types, tumor differentiation, lymphatic invasion, venous invasion, tumor budding, and node metastasis were univariately analyzed by log-rank test. Then a multivariate analysis was performed to identify independent prognostic factors using Cox proportional hazards model. Results: We classified the depth beyond mp into 2 groups (S group (n=127); < 6 mm, D group (n=69); 6 mm=< ). In univariate analysis, five year survival rate for S and D group were 71% and 50%, respectively (p=0.0008). Lymphatic invasion (mild vs. severe; 76% vs. 50%; p=0.0049), venous invasion (mild vs. severe; 71% vs. 48%; p=0.0036), tumor budding (mild vs. severe; 71% vs. 50%; p=0.0167) and node metastasis (negative vs. positive; 81% vs. 50%; p< 0.0001) were also significantly associated with five year survival after curative surgery. In a multivariate analysis with these factors, node metastasis (p=0.0052, 95%Cl 1.25-3.55, HR 2.11) and depth beyond mp (p=0.0434, 95%Cl 1.01-2.52, HR 1.60) were selected as significant prognostic factors. Five year survival rate with none, one, and both of these factors (node positive, D group) were 84%, 61%, and 38%, respectively (p< 0.0001). Conclusions: Subclassification of pT3 lower RC by the depth beyond mp (cut off value=6 mm) is very useful for predicting their prognosis as well as lymph node metastasis.

Key words
rectal cancer, prognostic factor, depth of tumor invasion

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Masayoshi Miyoshi Department of Surgery I, National Defense Medical College
3-2 Namiki, Tokorozawa city, 359-8513 JAPAN

Accepted
July 28, 2004

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