SP 3.10 Re-evaluating R1 Margins After Transanal Minimally Invasive Surgery: Implications on Management of Rectal Cancer

Abstract

Following transanal minimally invasive surgery (TAMIS), R1 margins reported based on the index specimen often prompt completion radical surgery. This study evaluates whether such cases represent true R1 resection and explores strategies to avoid unnecessary major resections.

A retrospective review was undertaken of all patients undergoing TAMIS for rectal neoplasia between 2018 and 2025 at single colorectal unit. Cases reported as R1 or equivocal were identified. The reason for margin status, subsequent management, local recurrence, and cancer-related mortality were assessed.

TAMIS was performed either laparoscopically or robotically (Lap-TAMIS n = 23; rTAMIS n = 8). Histopathology reported R1 margins in two rTAMIS T1 cancers and R1 or Equivocal margins in eight Lap-TAMIS cases. Robotic-TAMIS patients underwent endoscopic assessment with histology demonstrating granulation tissue; no residual malignancy. These patients were managed further with surveillance following multidisciplinary team (MDT) discussion. Among Lap-TAMIS patients, one underwent repeat TAMIS and three proceeded to radical resection; no residual carcinoma was identified in any oncological specimen. The remaining patients were managed with surveillance (equivocal margin in T1 cancer with no recurrence) and palliative intent (expected). No local recurrence was observed and there was no cancer-related mortality. The most common reason for incomplete margin status was diathermy artefact and specimen fragmentation.

R1 margins reported following TAMIS are frequently misinterpreted due to diathermy artefact. Accurate distinction between true R1 and equivocal/indeterminate margins is essential to avoid overtreatment. Reporting such margins as equivocal may better facilitate MDT-led decision-making and help prevent unnecessary radical surgery in early rectal cancer.