eP421 - Predictors of Positive Surgical Margins After Resection of Large Colonic Tumors

Purpose/Background: Tumor size has been recognized to be significantly associated with progression free and cancer specific survival in patients with colorectal cancer. The objective of this study was to determine the predictive factors associated with positive resection margins in large colonic tumors measuring >5 cm after colectomy.Methods/Interventions: This retrospective cohort study identified all patients with clinical stage I-III colonic adenocarcinoma >5 cm in size who underwent colectomy from the US National Cancer Database (2010-2019). Univariable and multivariable binary logistic regression analyses were conducted to determine the predictive factors of positive resection margin after colectomy. Main outcome measures were Factors independently associated with increased likelihood of positive margins and impact on overall survival.Results/Outcomes: 37,880 patients with large colonic tumors who underwent open (20,144; 56.3%), laparoscopic (14,457; 40.4%) or robotic-assisted resection (1,158; 3.2%) were included; 51.3% of patients were female and 48.7% male. The mean age was 68.6 ±14.2 years. Patients were followed up for a median of 61.1 [IQR: 27.3, 87.5] months. The majority of the tumors were located on the right colon (57.2%), followed by left colon (30.9%) and transverse colon (11.9%). The most common facility type was Comprehensive Community Cancer Program (44.1%), followed by Academic/Research Program (26.1%).On multivariable analysis, the independent predictors of positive resection margins were undergoing surgery at a comprehensive community cancer program (OR: 1.51, 95%CI: 1.33- 1.71, p < 0.001) and community cancer program (OR: 1.42, p < 0.001), stage II disease (OR: 1.55, 95%CI:1.34-1.79, p < 0.001), stage III disease (OR: 2.17, 95%CI:1.87- 2.5, p < 0.001), mucinous carcinomas (OR: 1.22, p=0.003), signet-ring cell carcinomas (OR: 1.49, p=0.005), higher tumor grade (G3: OR=1.87, 95%CI: CI 1.5- 2.32, p < 0.001; G4: OR= 1.71, 95%CI: 1.29- 2.28, p < 0.001), lymphovascular invasion (OR:2.23, 95%CI 2.01- 2.48, p < 0.001), perineural invasion (OR: 1.83, 95%CI: 1.62- 2.06, p < 0.001) and receiving neoadjuvant chemotherapy (OR: 1.6, p=0.016). Conversely, the laparoscopic approach (OR: 0.69; 95%CI: 0.62-0.76; p < 0.001) and robotic-assisted approach (OR: 0.721, 95%CI: 0.53-0.98, p=0.038) were independently associated with lower odds of positive margins. Study limitations were its retrospective nature that is associated with selection bias, only CoC-accredited hospitals were included in the analysis, and some factors that may affect outcomes, including body mass index and surgeons’ experience, were not accounted for in the model used.Conclusion/

Discussion: Stage II and III, community cancer program, higher tumor grade, lymphovascular and perineural invasion, signet ring cell and mucinous histology and receiving neoadjuvant chemotherapy significantly increased the risk of positive margins after colectomy in patients with large colonic cancers. Minimally invasive surgery may significantly decrease the odds of positive margins.