Involvement of tissue changes induced by neoadjuvant treatment in total mesorectal excision (TME): novel suggestions for determining TME quality.

backgroundFew studies to date have investigated morphological changes after neoadjuvant treatment (NAT) and their implications in total mesorectal excision (TME). This study was primarily designed to evaluate whether tissue changes associated with NAT affected the quality of TME and additionally to suggest a more objective method evaluating TME quality.

methodsThis study enrolled 1322 consecutive patients who underwent curative robot-assisted surgery for rectal cancer. Patients who did and did not receive NAT were subjected to propensity-score matching, yielding 402 patients in each group.

resultsNAT independently reduced complete achievement of TME [odds ratio (OR) = 2.056, p = 0.017]. Intraoperative evaluation identified seven tissue changes significantly associated with NAT, including tumor perforation, mucin pool, necrosis, fibrosis, fat degeneration, and rectal or perirectal edema NAT (p < 0.001-0.05). Tumor perforation (OR = 5.299, p = 0.001) and mucin pool (OR = 14.053, p = 0.002) were independently associated with inappropriate (near-complete + incomplete) TME. Complete TME resulted in significantly reduced local recurrence (4.3% vs 15.3%, p = 0.003) and increased 5-year DFS rate (80.6% vs 67.6%, p = 0.047) compared with inappropriate one. By contrast, two tiers of complete and near-complete TMEs vs incomplete TME did not. Notably, among patients with complete TME, those who received NAT had a lower 5-year DFS than those who did not (77.8% vs 83.3%, p = 0.048).

conclusionsNAT-associated tissue changes, somewhat interrupting complete TME, may provide unsolved clue to the relative inability of NAT to improve overall survival. The conventional three-tier grading of TME seems to be simplified into two tiers as complete and inappropriate.