To explore the feasibility and outcomes of endoscopic intermuscular dissection (EID), a new endoscopic approach, we present a case series of EID in patients with suspected deep submucosal invasive T1 rectal cancers based on pre-interventional assessment. This series aims to describe the potential role of EID in risk-adapted treatment strategies for early rectal cancers.

EID was performed in sixteen patients at the endoscopy departments of the University Hospitals Augsburg and Bochum. Procedures were carried out using the Olympus CZ-1500 gastroscope and the Olympus EVIS X1® system. En bloc resection of the lesion was achieved in all cases. In six patients, the resection site was closed using the Olympus SutuArt® hand-suturing device.

Sixteen patients underwent EID. In all cases, the lesions were removed without significant complications. Histopathological examination confirmed low-grade adenocarcinomas with deep submucosal invasion, low tumor budding, and no lymphovascular invasion in six cases and low-grade adenocarcinoma with superficial submucosal invasion, low tumor budding and no lymphovascular invasion in one case. In one case the adenocarcinoma was previously treated with TNT. Histology showed a low grade T1 carcinoma with intermediate tumor budding and histological evidence of perineural invasion. In one case histology confirmed a T2 carcinoma with poor differentiation (G3).

The other cases showed tubular adenoma with high-grade dysplasia in three cases and low-grade dysplasia in another two cases. Furthermore, there was one neuroendocrine tumor and one vascular malformation removed with EID.

Fourteen of the sixteen resections achieved clear margins. In one patient with confirmed deep-submucosal invasive cancer (D-SMIC), an R1 resection had to be presumed at the deep margin due to a specimen tear. This patient subsequently underwent a surgical transanal full-thickness resection. Histopathological analysis of the surgical specimen revealed no residual tumor cells.

In the specimen of the rectal carcinoma previously treated with total neoadjuvant therapy, histological examination identified infiltration of smooth muscle fibers. Consequently, an R1 resection had to be assumed.

This case series demonstrates that endoscopic intermuscular dissection is a promising approach for the management of rectal D-SMIC. The technique allowed for successful resection in all cases, with no significant complications. 

Recognizing the potential of EID as an alternative to radical surgery, we are actively engaged in collecting and structuring additional data to strengthen the evidence base for its use. Ongoing analysis will aim to assess its outcomes in larger patient cohorts and refine patient selection criteria to maximize safety and effectiveness.