Flattened Tumor Requires a More Careful Attention for Residual Distal Cancer Spread in Locally Advanced Lower Rectal Carcinoma after Chemoradiotherapy

Abstract

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.

Impact of Microscopically Positive (≤1 mm) Distal Margins on Disease Recurrence in Rectal Cancer Treated by Neoadjuvant Chemoradiotherapy

“…The present study highlights that a pathologic finding of a distal margin of ≤1 mm is not related to lower 5-year LRRFS in patients with a major response or pCR (87.0% vs. 94.7%, p = 0.77), provided that R0 resection is achieved [ 21 ], but a worse LRRFS was observed with a distal margin of ≤1 mm in TRG3–5 patients (68.5% vs. 84.2%, p = 0.027). In other words, a ≤1 mm clear margin width seems to be inadequate in low responders, probably due to the overwhelmingly high risk of residual tumor burden beyond the distal edge of the tumor [ 22 , 23 , 24 ]. Indeed, a distal margin of ≤1 mm in low responders means not only a higher risk of mucosal/submucosal spread of tumor over the resection edge, but also a higher likelihood of incomplete mesorectal excision with possible residual nodal disease [ 25 ], despite similar mean numbers of harvested nodes being observed with close vs. clear margins (14.6 vs. 15.1, p = 0.604).…”

Preoperative chemoradiotherapy using S-1 combined with celecoxib for advanced lower rectal cancer: Phase I/II study

“…In the present study, the anal sphincter preservation rate was 31.6%, which was lower than in other reports of CRT for rectal cancer [8][9][10] . The distal spread of the tumor cells was reported to remain in some cases, even though the tumor had been flattened 31) . Therefore, the resecting range was not reduced from that assumed before CRT at our institution.…”