Clinical Management of Patients with Colorectal Intramucosal Carcinoma Compared to High-Grade Dysplasia and T1 Colorectal Cancer.

Background and aims: In the colorectum, intramucosal carcinoma (IMC), like high-grade dysplasia (HGD), should be resected endoscopically. We were interested to understand how real-world treatment of IMC cases compares to management of HGD and T1 colorectal cancer (CRC).

Methods: A multicenter cohort study was conducted. Through pathology databases, all patients diagnosed between 2010-2019 with HGD, IMC or T1 CRC polyps at three hospitals in a regional Canadian center were identified. The primary outcome was the proportion of surgical management of IMC compared to HGD after complete endoscopic resection. Secondary outcomes were the proportion of synchronous advanced neoplasia (SAN) and the adjusted hazard ratios (aHR) for metachronous advanced neoplasia (MAN) in the three groups among patients eligible for follow-up.

Results: We identified 753 patients with IMC or HGD on a first pathology diagnosis, including 601 after complete endoscopic resection. Patients with IMC were more likely to undergo surgery after complete endoscopic resection compared to patients with HGD (10.5% [6/57] vs 0% [0/544], p<0.001). 455 patients had follow-up endoscopy and pathology (mean age 67.1y, 42.2% female, median follow-up 3.4y): 269 with HGD, 60 with IMC, 126 with T1 CRC. Proportions of SAN were 24.2%, 26.7% and 25.4% (p=0.908). Compared to HGD, patients with IMC and T1 CRC had similar MAN risks (aHR 0.82 [0.43-1.59] and aHR 1.16 [0.66-2.05], respectively). No lymph nodes were positive (0/363) and no metastasis occurred among patients with IMC.

Conclusions: Patients diagnosed with colorectal IMC were more likely to undergo surgery after complete endoscopic resection than when HGD was diagnosed, although they were not at increased risk of SAN or MAN in this study and the known risk of nodal metastasis with colorectal IMC is small (0-2%). Unless a patient diagnosed with IMC is particularly concerned with this small risk, complete endoscopic resection should be considered definitive treatment for IMC and should not be followed by surgery.