Distinct prognostic impact of circumferential resection margin and adverse histologic features after intersphincteric resection for ultra-low rectal cancer following chemoradiotherapy: a retrospective cohort study.

PURPOSE: Circumferential resection margin (CRM) involvement after intersphincteric resection (ISR) is uncommon but clinically important. We evaluated the association of CRM status and adverse histopathologic features with recurrence after ISR following neoadjuvant concurrent chemoradiotherapy (CCRT).

METHODS

From 2011 to 2022, 520 patients underwent ISR for ultra-low rectal cancer (≤3 cm from the anal verge) at a single tertiary center. Among them, 326 who received CCRT were analyzed. Clinicopathologic variables were evaluated in relation to disease-free survival (DFS), local recurrence-free survival (LRFS), and distant recurrence-free survival (DRFS). Multivariable Cox regression evaluated adjusted associations.

RESULTS

CRM involvement occurred in 8 patients (2.5%). Fifty-four patients (16.6%) developed recurrence: 17 local only, 34 distant only, and 3 both. Five-year DFS, LRFS, DRFS, and overall survival were 74.8%, 87.5%, 85.5%, and 91.4%, respectively. CRM involvement was associated with inferior DFS (45.0% vs. 75.8%, P = 0.018) and LRFS (52.5% vs. 88.6%, P < 0.001), but not DRFS (72.9% vs. 85.8%, P = 0.299). After adjustment, CRM involvement remained associated with LRFS (hazard ratio [HR], 9.419; P < 0.001) and DFS (HR, 3.612; P = 0.017). Perineural invasion was associated with all recurrence endpoints.

CONCLUSION

CRM involvement was associated predominantly with poorer local control after ISR following CCRT, whereas adverse microscopic features, particularly perineural invasion, showed broader associations with both local and distant recurrence. The combined assessment of CRM status and microscopic tumor invasiveness may therefore provide complementary prognostic information after ISR for ultra-low rectal cancer.