EP637 - Side to Side Comparison of Stage II/III Colon Cancer in Young Patients: A National Cancer Database (NCDB) Audit

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Purpose/Background: Early onset colorectal cancer (EoCRC) is generally considered Colorectal Cancer (CRC) diagnosed between 18 – 49 years old. This was in concordance with the United States national guideline recommendation for first screening colonoscopy at age 50 for average risk patients. In 2021, the recommendation changed to age 45 due to benefit observed in screening younger, asymptomatic patients. With the screening age change, there may be benefit in defining EoCRC as patients < 45 years old.
Tumors in the proximal colon (right side) and distal colon (left side) exhibit different molecular characteristics and histology. Additionally, prior work has noted significant demographic and survival differences between right- and left-sided colon cancers. Stage for stage differences are impacted by adjuvant treatment. Our goal was to determine the incidence, characteristics, and outcomes across right- and left-sided Stage II/III CRC in patients less than 45 years old.

Methods/Interventions: The NCDB was reviewed from 2018-2021 to identify young (>18 and < 45 years) patients who underwent elective major colon resection for Stage II and III colon adenocarcinoma. Patients were stratified into right- versus left-sided colon cancer. Univariate analysis compared patient demographics, tumor biology, and adjuvant treatment compliance between right- and left-sided resections. Multivariate analysis was done analyzing differences in readmission as well as survival, while controlling for significant covariate differences between right and left sided colon cancer groups. A subgroup analysis was performed to assess for differences between the right- and left-sided cohorts and adjuvant treatment compliance. Our main outcome measures were the rate and impact of right- versus left-sided colon cancer characteristics and outcomes in young patients.

Results/Outcomes: Of 4,815 selected patients, 1,869 (39%) had right-sided and 2,946 (61%) had left-sided colon cancers. Both right and left sided cancers were predominantly Stage III, but this difference was more substantial in left sided cancers (37% Stage II versus 63% Stage III P< 0.001). Only right-side had a significant gender imbalance with 58% male patients (P < 0.001). Left-side had fewer KRAS mutations (33% vs. 50% right; P< 0.001). Right-side was more likely to have microsatellite instability-high status (MSI-H) (89% vs. 70%; P< 0.001). Left-side was more likely to have poor prognostic histologic features. On multivariate analysis, there was a statistically significantly longer in-patient stay and longer time between diagnosis and systemic therapy in the left sided group; the clinical differences were minor however. There were no survival differences. Subgroup analysis noted 13% non-compliance to recommended adjuvant chemotherapy, with significant insurance and race differences between groups.

Conclusion/Discussion: Young patients who required colectomy for right- and left-sided colon cancer differed in incidence, demographics, and tumor biology. Our study demonstrated both KRAS mutation and MSI-H status was more likely in right-sided colon cancers, as well as an unacceptably high rate of non-compliance to recommended adjuvant treatment in patients < 45 years old. Given these results, further study of EoCRC-specific patient and tumor characteristics is critical to providing individualized care and potentially improving outcomes.