To determine the prevalence of submucosal invasive cancer and assess curative endoscopic resection outcomes for large low-risk LNPCPs (≥20 mm) located in the left colon.

A prospective multicentre cohort of patients referred for ER of LNPCPs between October 2008 and February 2025 was reviewed. All centres were tertiary referral hospitals performing both endoscopic mucosal resection (EMR) and endoscopic submucosal dissection (ESD). The left colon was defined as rectosigmoid to the splenic flexure inclusive. The primary outcome was to determine the rate of endoscopically curable SMIC in left colon LNPCPs.

867 patients with sporadic left colon LNPCPs were included (median age 68, gender male 440 (50.7%)). 842 underwent ER, and 25 did not have ER attempted due to either suspicion of deep SMIC (n=22) or technical reasons (n=3). Of those that underwent ER, SMIC was present in 100/842 (11.9%), and in those who went direct to surgery, the SMIC rate was 16/25 (64.0%). Thus, the overall rate of SMIC was 116/867 (13.4%). 105/116 (90.5%) cancers had full histopathological data to assess endoscopic curability. 13/105 (12.4%) were considered low-risk. The rate of endoscopically curable SMIC of the entire cohort analysed was 13/856 (1.5%)

In a large Western multicentre cohort, the rate of SMIC in left colon LNPCPs was 13.4%. Endoscopically curable cancer was 1.5%. A selective resection algorithm that identifies curable SMIC is required to facilitate selection between different ER modalities.