The subserosal elastic lamina: an anatomic landmark for stratifying pT3 colorectal cancer

Approximately 50 percent of all patients with resected colorectal carcinoma have tumors with pT3 status; however, no subclassifications of the penetration depth have been proposed. The purpose of this study is to evaluate the significance of histologic invasion beyond subserosal elastic lamina by colorectal carcinoma for postoperative recurrence and long-term survival after resection.

pT3 colorectal carcinomas located above the peritoneal reflection were retrospectively classified into two depth grades (subserosal elastic lamina classification). Namely, "pT3-shallow" is defined as tumors those are confined above the subserosal elastic lamina, and "pT3-deep" is defined as tumors those penetrate beyond it. Based on subserosal elastic lamina classification, the 325 consecutive patients who underwent resections were divided into two groups, and then the clinicopathologic features, incidence of postoperative recurrence, and survival rates were compared between the two groups.

The overall postoperative recurrence rate in the pT3-deep group (35.2 percent) was higher than that in the pT3-shallow group (20.8 percent). In detail, liver and peritoneal recurrence rates in the pT3-deep group (19.7 percent, 7.7 percent, respectively) were higher than those in the pT3-shallow group (9.4 percent, 2.0 percent, respectively). There was a strong difference ( P < 0.0001) in overall survival rate between the pT3-deep group (5-year survival of 57.0 percent) and the pT3-shallow group (5-year survival of 78.6 percent). Multivariate analysis revealed that synchronous hematogenous metastasis ( P < 0.0001), lymph node metastasis ( P < 0.05), venous invasion ( P < 0.01), and subserosal elastic lamina classification ( P < 0.05) were the independent prognostic factors for postoperative survival.

The newly proposed subserosal elastic lamina classification is a useful subclassification to predict the prognosis of patients with resected pT3 colorectal carcinomas.