Consequences of omitting additional treatment after local excision of high-risk early rectal cancer: a national cohort.

PURPOSE: This study aimed to evaluate oncological outcomes in patients with high-risk early rectal cancer undergoing local excision, comparing those who received guideline-recommended additional treatment to those who did not, either due to comorbidities or personal preference. METHOD: National data on patients treated by transanal endoscopic microsurgery (TEM) or transanal minimally invasive surgery (TAMIS) for early rectal cancer without prior chemoradiotherapy between 2010 and 2020 were analyzed retrospectively. Patients were classified into low-risk (pT1 without risk factors for lymph node involvement) and high-risk (pT1 with risk factors and all pT2). High-risk patients receiving additional treatment (mainly completion TME, or less frequently adjuvant chemoradiotherapy for high-risk pT1) were compared to those without further treatment. Endpoints were 5-year relative survival, disease-free survival, overall survival, local recurrence, and distant recurrence. RESULTS: Among 298 patients, 70 (23.5%) were low-risk pT1, 153 (51.3%) were high-risk pT1, and 75 (25.2%) were pT2. Additional treatment was omitted in 93 (60.8%) of high-risk pT1 and 39 (52.2%) of pT2 cases. Compared to patients following guidelines, those not receiving additional treatment had lower 5-year disease-free survival of 53.3% vs. 80.9% (p = 0.008) and higher 5-year local recurrence rates of 22.0% vs. 7.3% (p = 0.008). Five-year overall survival was 63.9% vs. 90.6% (p = 0.013), and relative survival 81.9% vs. 97.7% (p = 0.157). CONCLUSION: Omitting indicated additional treatment following TEM or TAMIS for high-risk early rectal cancer is associated with a substantially higher local recurrence rate and loss of long-term disease-free survival and overall survival.