BACKGROUND/AIMS: Limited data are available on distal resection margin (DRM) for lower rectal cancer (LRC) after preoperative chemoradiotherapy (pre-CRT); thus, we aimed to establish the criteria for DRMs as estimated by the macroscopic tumor appearance. METHODS: This was a pathological study using whole-mount sections that included the entire circumference of tumor. Residual cancer spread located most distally from the macroscopic tumor border was mainly evaluated. RESULTS: A retrospective cohort of 42 consecutive patients with locally advanced LRC after pre-CRT was enrolled, and 38 patients were eligible for this study. According to the macroscopic tumor appearance, 18 patients had raised-type and 20 had flattened-type tumors. Patients with flattened-type tumors were closely associated with histopathological regression grade. Residual distal cancer spread (RDCS) was located ≤4.0 mm (median, 0.1 mm) in the raised-type tumors and ≤17.1 mm (median, 4.2 mm) in the flattened-type tumors. RDCS in flattened-type tumors was distributed diffusely and distally from the tumor border (p = 0.022). CONCLUSION: Even in patients evaluated as pre-CRT responders, flattened tumors often accompanied distally located residual cancer that had spread from the tumor border and require more careful attention in order to ensure cancer clearance.
BACKGROUND/AIMS: Limited data are available on distal resection margin (DRM) for lower rectal cancer (LRC) after preoperative chemoradiotherapy (pre-CRT); thus, we aimed to establish the criteria for DRMs as estimated by the macroscopic tumor appearance. METHODS: This was a pathological study using whole-mount sections that included the entire circumference of tumor. Residual cancer spread located most distally from the macroscopic tumor border was mainly evaluated. RESULTS: A retrospective cohort of 42 consecutive patients with locally advanced LRC after pre-CRT was enrolled, and 38 patients were eligible for this study. According to the macroscopic tumor appearance, 18 patients had raised-type and 20 had flattened-type tumors. Patients with flattened-type tumors were closely associated with histopathological regression grade. Residual distal cancer spread (RDCS) was located ≤4.0 mm (median, 0.1 mm) in the raised-type tumors and ≤17.1 mm (median, 4.2 mm) in the flattened-type tumors. RDCS in flattened-type tumors was distributed diffusely and distally from the tumor border (p = 0.022). CONCLUSION: Even in patients evaluated as pre-CRT responders, flattened tumors often accompanied distally located residual cancer that had spread from the tumor border and require more careful attention in order to ensure cancer clearance.