Is the underwater injection endoscopic mucosal resection technique suitable for T1 colorectal cancer?

10.1055/a-2479-9227

We read the article by Hirai et al. [1] with great interest and appreciate the authors' innovative approach; however, we would like to raise several concerns and seek clarification on a few points.

First, when evaluating the feasibility of a novel technique, the study design should ideally be prospective. Retrospective studies are more appropriate for well-established methods [2]. Therefore, a prospective study should be conducted initially to adequately assess the safety and efficacy of the new technique before performing retrospective analyses.

Second, according to the European Society of Gastrointestinal Endoscopy (ESGE) guidelines, endoscopic submucosal dissection (ESD) should be considered for colorectal lesions with suspected submucosal invasion, particularly those >20 mm [3]. In the study reported by Hirai et al., some T1 colorectal cancers (CRCs) exceeded 20 mm in diameter. It remains unclear why underwater injection endoscopic mucosal resection (UIEMR) was still selected for these cases. Although UIEMR demonstrates a relatively high en bloc resection rate, its R0 resection rate is lower, increasing the likelihood of Rx resection. In such cases, ESD or hybrid ESD might be more appropriate options.

Third, in order to evaluate whether the novel technique can achieve adequate vertical margins in T1 CRC, the authors included 135 lesions in total, of which only seven were histologically confirmed to be T1 CRC. Drawing conclusions from such a limited number of relevant cases may compromise the reliability of the findings. Inclusion of a larger cohort of confirmed T1 CRC cases is necessary for more robust conclusions.

Lastly, among the seven T1 CRC lesions, several showed submucosal invasion depths >3000 μm, and the vertical margin distance extended even further. This raises the question of whether the UIEMR resection depth may have exceeded the submucosal layer and potentially damaged the muscularis propria [4].

In conclusion, despite these concerns, UIEMR appears to offer a promising new approach for the resection of colorectal polyps ≥10 mm and warrants further clinical investigation and validation.

Publication History

Article published online:
28 October 2025

• References

• 1 Hirai Y, Toyoshima N, Takamaru H. et al. Procedural outcomes of a novel underwater injection endoscopic mucosal resection technique for colorectal polyps ≥10 mm. Endoscopy 2025; 57: 494-499
• 2 Grimes DA, Schulz KF. An overview of clinical research: The lay of the land. Lancet 2002; 359: 57-61
• 3 Pimentel-Nunes P, Libânio D, Bastiaansen BAJ. et al. Endoscopic submucosal dissection for superficial gastrointestinal lesions: European Society of Gastrointestinal Endoscopy (ESGE) Guideline – Update 2022. Endoscopy 2022; 54: 591-622
• 4 Mesa H, Drawz S, Dykoski R. et al. Morphometric measurement of submucosal thickness in areas of fat deposition in the terminal ileum and colonic sections, with correlation with body mass index, weight and age: a male autopsy study. Histopathology 2015; 67: 457-463