Stepwise organ-preserving management of incidental pT1 rectal adenocarcinoma: outcomes after completion transanal endoscopic microsurgery (TEM)

Background: Accurate in vivo assessment of rectal lesion invasion remains challenging despite advances in high-definition endoscopy and AI-assisted diagnostics. Some lesions resected endoscopically for presumed superficial pathology are ultimately found to contain submucosal invasive adenocarcinoma (pT1), prompting reconsideration of treatment. While total mesorectal excision (TME) remains the standard for radical oncologic removal, its morbidity has increased interest in organ-preserving approaches such as transanal endoscopic microsurgery (TEM). Methods: We conducted a retrospective, single-centre study including all consecutive patients who underwent TEM after endoscopic mucosal resection (EMR) or endoscopic submucosal dissection (ESD) of rectal lesions unexpectedly diagnosed as pT1 adenocarcinoma. Patients treated between 1995 and 2024 with at least 12 months of follow-up were included. Primary endpoints were overall survival (OS) and disease-free survival (DFS); secondary endpoints included residual disease in the TEM specimen and patterns of recurrence. Results: Sixty-six patients were included. TEM identified residual dysplasia in 25 patients (37.9%) but no cases of residual invasive carcinoma. Surgical margins were clear in all cases. Only one patient (1.5%) required salvage TME due to adverse histological features. At a median follow-up of 15 months, OS was 100% and DFS 97%, with two patients (3%) experiencing local recurrence successfully managed with salvage surgery. No distant metastases were observed. No stoma formation or major complications occurred. Conclusions: In patients with incidental pT1 rectal adenocarcinoma following EMR or ESD, completion TEM provides excellent short-term oncological outcomes with minimal morbidity. This two-step, organ-preserving approach appears oncologically adequate in well-selected low-risk patients and offers a viable alternative to radical surgery, especially when maintaining function is a priority.