E108: Risk Factors for a Positive Resection Margin in Locoregional Appendix Cancer and its Impact on Survival: the National Cancer Database Analysis

The impact of a positive resection margin (RM+) in appendiceal cancer remains unclear. While some small studies suggest RM+ does not correlate with worse survival in low-grade mucinous appendiceal cancer, solid data are lacking. We aimed to assess the RM+ rate in appendix cancer, its risk factors, and survival impact, as colon cancer data cannot be extrapolated due to differences in tumor biology.

Methods:

We conducted a multicenter retrospective cohort study using the National Cancer Database (2004-2019). Stage I-III appendix cancer was included. The association between hypothesized predictors and RM+ after definitive surgery was analyzed with stepwise logistic regression. RM+ impact on overall survival (OS) was assessed with the Kaplan-Meier method and Cox regression. Subgroup analysis was performed among low/high grades and mucinous/non-mucinous pathology.

Results:

Overall, 6,800 patients were identified: 737 (10.8%) with RM+ and 6,063 (89.2%) with RM-. RM+ patients more commonly had signet ring cell pathology (13.3% vs 7.4%, p< 0.01), pT4 disease (68.1% vs 34%, p< 0.01), and positive LNs (33.8% vs 20.6%, p< 0.01) than RM- patients. Appendectomy or ileocecectomy was more common in RM+ (40.3% vs 28.5%) whereas right hemicolectomy was more common in RM- (59.7% vs 71.5%) (p< 0.01). RM+ patients more commonly received pre- (4.2% vs 1.7%, p< 0.01) and postoperative chemotherapy (49.8% vs 37.3%, p< 0.01).

In multivariable analysis, pT3 (ref. pT1-2; OR 4.92; 95%CI 2.38-10.18), pT4 (OR 20.75; 95%CI 10.21-42.17), positive LNs (OR 1.87; 95%CI 1.52-2.31), and high-grade histology (OR 1.32; 95%CI 1.06-1.64) were associated with RM+ while right hemicolectomy (ref. appendectomy or ileocecectomy; OR 0.62; 95%CI 0.50-0.77) was associated with RM-.

Median OS was shorter in patients with RM+ (54 months vs not reached, p< 0.01). Median OS was significantly different between RM+ and RM- in all subgroups: low-grade (p< 0.01) and high-grade mucinous (p< 0.01), low-grade (p< 0.01) and high-grade (p< 0.01) non-mucinous, and signet ring cell carcinoma (p< 0.01) (Figure 1). RM+ was associated with worse OS after adjustment to other factors (HR 1.76; 95%CI 1.47-2.12).

Conclusions:

RM+ correlates with worse survival in all subtypes of stage I-III appendix cancer including low-grade mucinous pathology. Right hemicolectomy and more extensive surgery are associated with RM-. General surgeons and surgical oncologists should prioritize achieving negative margins at definitive surgery for all histological subtypes of appendiceal cancer.