EP675 - Recurrence at the Reconnection: Characteristics and Genetics of Anastomotic Recurrence in Colorectal Cancer

Purpose/Background: Anastomotic recurrence after colon cancer resection is uncommon (0.4%–2%) but clinically significant, typically occurring two to three years post-surgery. Associated risk factors include advanced nodal stage, mucinous histology, lymph-vascular invasion, margin status, and anastomotic leakage, though causal links remain unclear. Surgical resection may benefit patients with localized recurrence, but delayed detection often reduces curative options. Limited evidence, inconsistent definitions, variable follow-up, and absence of molecular markers hinder accurate assessment of incidence and risks. This study reviews all anastomotic recurrence cases at a single institution and conducts molecular analysis to inform prevention and follow-up strategies. Current literature has not identified association between specific sporadic tumor mutations and risk of recurrence, but common mutations include APC, KRAS, TP53, PIK3CA, ATM, and PIK3R1.

Methods/Interventions: Following IRB approval, all adult colon resections with anastomotic recurrences identified between 1/1/2015 and 6/1/2025 at a single institution were retrospectively evaluated. Cases with incomplete records were excluded. Typical demographic and clinicopathologic data were collected to include, but not be limited to tumor pathology, treatment information, and outcomes. Univariate analyses using Kaplan Meyer curves and hazard ratios were performed.

Results/Outcomes: Overall, 27 patients were identified (original carcinomas: 74% colon and 26% rectum); 36% and 32% demonstrated lymph-vascular invasion and perineural invasion, respectively. Decreased disease-free survival was noted with lymph-vascular invasion (p=0.0004), increasing tumor size (p=0.0466), and increasing number of positive lymph nodes (p=0.0027). 91% of initial tumors were stable when tested for microsatellite instability (n=23). One of these microsatellite stable cases resulted with a KRAS mutation. Genetic analysis is pending on recurrent tumors.

Conclusion/Discussion: Anastomotic recurrence presents a persistent clinical challenge with unclear causes. Consistent with published reports, lymph-vascular invasion, tumor size and positive nodes appear to increase the risk of recurrence and are associated with poor outcomes. The next step in analysis is to identify specific mutations present in recurrent tumors to inform mutations that may predispose patients to risk of anastomotic recurrence.