Lymphovascular Infiltration, Not Depth of Invasion, is the Critical Risk Factor of Metastases in Early Colorectal Cancer: Retrospective Population-based Cohort Study on Prospectively Collected Data, Including Validation.

OBJECTIVE To identify clinical and histopathological risk factors of LNM in T1 CRC. SUMMARY OF BACKGROUND DATA The requisite of additional surgery after locally resected T1 CRC is dependent on the risk of LNM. Depth of submucosal invasion is used as a key predictor of lymphatic metastases although data are conflicting on its actual impact. METHODS Retrospective population-based cohort study on prospectively collected data on all patients with T1 CRC undergoing surgical resection in Sweden, 2009-2017 and Denmark 2016-2018. The Danish cohort was used for validation. Potential risk factors of LNM investigated were; age, sex, tumor location, submucosal invasion, grade of differentiation, mucinous subtype, lymphovascular, and perineural invasion. RESULTS One hundred fifty out of the 1439 included patients (10%) had LNM. LVI (P < 0.001), perineural invasion (P < 0.001), mucinous subtype (P = 0.006), and age <60 years (P < 0.001) were identified as independent risk factors whereas deep submucosal invasion was only a dependent (P = 0.025) risk factor and not significant in multivariate analysis (P = 0.075). The incidence of LNM was 51/882 (6%) in absence of the independent risk factors. The Danish validation cohort, confirmed our findings regarding the role of submucosal invasion, LVI, and age. CONCLUSIONS This is a large study on LNM in T1 CRC, including validation, showing that LVI and perineural invasion, mucinous subtype, and low age constitute independent risk factors, whereas depth of submucosal invasion is not an independent risk factor of LNM. Thus, our findings provide a useful basis for management of patients after local excision of early CRC.