S666 Comparing the Risk of Metachronous Advanced Neoplasia on Post-Operative Surveillance Lower Endoscopy in Patients With Early Onset vs Average Onset Colorectal Cancer

Introduction: Whether the post-operative risk of metachronous advanced neoplasia (MAN) differs between patients with early-onset colorectal cancer (EOCRC: <50 years) and average-onset colorectal cancer (AOCRC: ≥50 years) is inconclusive. We compared the characteristics of patients with EOCRC and AOCRC, postoperative surveillance lower endoscopy findings, and identified factors associated with MAN. Methods: Patients with EOCRC and AOCRC randomly selected at 1:2 ratio, matched ± 6 months at time of diagnosis, treated surgically at Cleveland Clinic between 2011 – 2021 with ≥1 post-operative surveillance lower endoscopy performed ≥6 months after surgery were included. Inflammatory bowel disease, hereditary colorectal cancer syndromes, and total proctocolectomy patients were excluded. Post-op endoscopic findings were categorized as: 1) Normal: no polyps/hyperplastic polyps <10 mm, 2) Non-advanced neoplasia (NAN): tubular adenoma <10 mm, sessile serrated adenoma <10 mm without dysplasia 3) Advanced neoplasia: serrated polyps ≥10 mm or with dysplasia, tubular adenoma ≥10 mm or with high-grade dysplasia or villous features, or CRC. Distal CRC was defined as CRC in the descending or sigmoid colon. Clinical features and surveillance endoscopy findings were compared by Fischer’s, Pearson’s chi-square, Wilcoxon, and t tests. Categorical variables were presented as percentages and continuous variables as median and IQR. Results: 230 EOCRC patients and 504 AOCRC patients diagnosed at a median age of 44 and 66 years were included. Sex, race, ethnicity, BMI, and alcohol use were similar between groups. Tobacco use, hyperlipidemia, hypertension, diabetes, aspirin/statin use and history of non-CRC were significantly commoner in the AOCRC group. Vitamin D levels were significantly lower in EOCRC patients. MAN was similar between groups, 13% in EOCRC vs 16.1% in AOCRC (P = 0.342). EOCRC patients had longer median post-op follow-up and fewer months between exams. On univariate analysis, MAN was not associated with age but with prior tobacco use, hyperlipidemia, and a history of distal CRC. Conclusion: EOCRC patients undergo fewer months between 1st and follow-up surveillance lower endoscopy; however, the incidence of MAN is no different than AOCRC. Smoking, hyperlipidemia, and distally located primary CRC are associated with MAN. These data corroborate some previous studies and support similar post-operative CRC surveillance strategies for EOCRC and AOCRC patients.