eP177 - Incidence of Venous Thromboembolism After Abdominoperineal Resection for Anal Squamous Cell Carcinoma – Is There a Need for Extended Prophylaxis?

Purpose/Background: Venous thromboembolism (VTE) is associated with significant morbidity and colorectal surgery patients - given the extent of pelvic surgery - are at increased risk for VTE in the post-operative period. Recent guidelines by the American College of Chest Physicians and the American Society of Colon and Rectal Surgeons have supported the use of extended VTE prophylaxis after discharge in cancer patients. While the incidence of postoperative VTE events in patients with inflammatory bowel disease (IBD) and rectal cancer is well described in the literature, characterization of VTE in patients undergoing abdominoperineal resection (APR) for anal squamous cell carcinoma (SCC) is scant. Our primary aim was to describe the incidence of VTE in anal SCC patients and identify associated risk factors. Our secondary aim was to compare VTE incidence in anal SCC patients to rectal cancer and IBD patients undergoing APR. We hypothesized that the incidence would be low in anal SCC patients but comparable to rectal cancer and IBD patients.Methods/Interventions: We queried the American College of Surgeons National Surgical Quality Improvement Program database from 2005 to 2021 for patients undergoing APR for anal SCC, IBD and rectal cancer. We collected data on the incidence of VTE (PE and DVT) events and identified patient factors associated with VTE events. We evaluated the incidence of VTE events over time, given the change in recommendations for extended VTE prophylaxis. Univariate and multivariable analyses were performed.Results/Outcomes: We identified 1,907 patients with anal SCC, 15,522 patients with rectal cancer and 2,580 patients with IBD who underwent APR from 2005 to 2021. The overall incidence of any VTE event was low across all groups and statistically not different (anal SCC n=36, 1.9%, IBD n=33, 1.3% and rectal cancer n=221, 1.4%, p=0.21). Readmission for VTE events was exceedingly rare and similarly, was not different across groups (anal SCC n=3, 0.2%, IBD n=2, 0.1% and rectal cancer n=23, 0.1%, p=0.66). The incidence of VTE events over time did not show a change for any group (p>0.8). VTE events in anal SCC patients occurred more commonly in patients with a partially dependent/totally dependent functional status compared to independent patients (5.2% vs. 1.4%, p < 0.001), surgical site infection (34.1% vs. 17.6%., p < 0.001) or sepsis or septic shock (16.9% vs. 5.1%, p < 0.001). When indication for APR was assessed on multivariable analysis, anal SCC patients were at similar risk for developing postoperative VTE compared to IBD and rectal cancer patients (p>0.2).Conclusion/

Discussion: The overall incidence of VTE events in anal SCC was low and was found to be comparable to patients undergoing APR for IBD and rectal cancer. Additionally, the incidence of readmission for VTE was very uncommon and suggests that post-discharge extended VTE prophylaxis may not be necessary. Future iteration of guidelines should reconsider the recommendation to prescribe extended VTE prophylaxis in light of the overall low event rate of VTE-related complications after APR.