Is pT2 subclassification feasible to predict patient outcome in colorectal cancer?

Background: This study aimed to evaluate the prognostic impact of pT2 subclassification according to the depth of muscularis propria (MP) invasion and to explore the clinicopathologic factors correlated with lymph node metastasis (LNM) and postoperative hematogenous metastasis in pT2 colorectal cancer.
Methods: A total of 317 patients with pT2 colorectal cancer were reviewed. pT2a represents the infiltration of the inner circumferential layer of the MP, and pT2b represents the infiltration of the outer longitudinal layer of the MP. Clinicopathologic factors and overall survival rates were compared in patients with pT2a and pT2b stage cancers. Multivariate analysis was performed to identify the significantly important prognostic factors. Univariate and multivariate analyses were performed, respectively, to identify the significantly important clinicopathologic factors correlated with LNM and postoperative hematogenous metastasis in pT2 colorectal cancer.
Results: According to the depth of MP invasion, 107 patients were classified as pT2a and 210 patients were classified as pT2b. Among them, there were 55 patients with LNM, 34 patients with postoperative hematogenous metastasis. There was significant difference in most of clinicopathologic features between patients in the pT2a and pT2b stages. Multivariate analysis identified pN stage (P < .001) and tumor location (P = .036) were independent factors affecting the prognosis. However, no apparent difference was observed between pT2a versus pT2b cancer. Univariate and multivariate analyses uniformly identified lymphovascular invasion (P = .035) and the depth of MP invasion (P = .005) as significantly correlated with LNM. Multivariate analysis found tumor location (P = .021) and the presence or absence of LNM (P < .001) were important factors affecting postoperative hematogenous metastasis.
Conclusions: In pT2 colorectal cancer treated with R0 surgery, there is a high risk of LNM in deep MP invasion versus superficial MP invasion. The pT2 subclassification system had no significant advantage in identifying a different prognosis, except for predicting the LNM before surgery. Rectal cancer and the presence of LNM were high-risk factors resulting in hematogenous metastasis postoperatively.