New risk factor classified by intramucosal polypoid/non-polypoid growth pattern in earlycolorectal cancer

The lymph node metastasis (LNM) rate of submucosal invasive colorectal cancer (pT1 CRC) is low (approximately 10%), even when the risk factors for LNM outlined in the Japanese Society for Cancer of the Colon and Rectum (JSCCR) guidelines for endoscopically resected lesions are present. To ensure that patients receive appropriate treatment, novel factors that link endoscopic and pathological diagnoses and more accurately predict LNM are needed. Polypoid growth (PG)/non-polypoid growth (NPG) classification, depth of submucosal invasion and stalk status are examples of such interconnected factors. This study investigated the association between LNM and the histological PG (hPG)/NPG (hNPG) classification in pT1 CRC. A total of 1059 consecutive cases with both sessile and pedunculated pT1 CRCs were examined. LNM was present in 126 (11.9%) patients. The hPG and hNPG types were observed in 49% (519/1059) and 51% (540/1059) of cases, respectively. Cohen's kappa coefficient for intra- and inter-observer agreement was 0.78. Multivariate analysis identified hNPG type (p < 0.001), positive lymphovascular invasion (LVI) (p < 0.001) and budding grade (BD) 2/3 (p < 0.001) as independent predictors of LNM. A new algorithm incorporating these three factors increased the predicted LNM rate to 16.0%, yielded an LNM prediction rate of 11.9%, compared with the 12.5% rate of the JSCCR algorithm. Notably, no LNM occurred in hPG lesions with negative LVI and BD 1, indicating that 25.8% (273/1059) of patients could have avoided additional surgery. Thus, hPG/hNPG classification may provide a simple and reproducible tool for refining LNM risk stratification in pT1 CRC.