Lymph node metastasis in T1 colorectal cancer with the only high-risk histology of submucosal invasion depth ≥ 1000 µm.

ABSTRACT

PURPOSE: The number of patients undergoing additional surgery after endoscopic resection (ER) for T1 colorectal cancer (CRC) is increasing. Regarding high-risk histology of lymph node metastasis (LNM) in T1 CRC, a submucosal invasion depth ≥ 1000 µm (T1b) alone may be related to a low incidence of LNM. This study was conducted to clarify the incidence of LNM and to identify factors associated with LNM in T1 CRC with high-risk histology characterized only by T1b. METHODS: We retrospectively investigated patients with pathological T1b CRC who underwent colorectal resection between 2010 and 2020. Patients were divided into two groups with high-risk histology those in whom the only high-risk feature was T1b (low-risk T1b group, n = 263), and those with T1b as well as lymphovascular invasion, tumor budding, or poorly differentiated or mucinous adenocarcinoma (high-risk T1b group, n = 289). The incidences of LNM and recurrence were compared. Multivariate analysis was performed to identify factors associated with LNM in the low-risk T1b group. RESULTS: The incidences of LNM were 3.8% and 21.6% in the Low- and High-risk T1b groups, respectively (p < 0.01), while the 5-year recurrence rates in the two groups were 0.6% and 3.4%, respectively (p = 0.10). Multivariate analysis revealed that only a predominant histological type of moderately differentiated adenocarcinoma (p = 0.04) was independently associated with LNM in the low-risk T1b group. CONCLUSION: When considering the omission of additional surgery after ER in cases of T1 CRC whose only high-risk histological feature is T1b, attention should be paid to the predominant histological type.