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Left-Sided Dominance of Early-Onset Colorectal Cancers: A Rationale for Screening Flexible Sigmoidoscopy in the Young

BACKGROUND: National databases show a recent significant increase in the incidence of colorectal cancer in people younger than 50. With current recommendations to begin average-risk screening at age 50, these patients do not have the opportunity to be screened. We hypothesized that most of the cancers among the young would be left sided, which would create an opportunity for screening the young by flexible sigmoidoscopy. OBJECTIVE: This study aims to analyze the anatomic distribution of sporadic colorectal cancers in patients under the age of 50. DESIGN: This is a retrospective review of a prospectively maintained database. SETTING: This study was conducted at a single high-volume tertiary referral center. PATIENTS: Patients under the age of 50 with colorectal cancer between the years 2000 and 2016 were included. Patients with IBD, familial adenomatous polyposis, Lynch syndrome, or hereditary nonpolyposis colorectal cancer were excluded. MAIN OUTCOME MEASURES: The primary outcomes measured were tumor location and stage, demographics, and family history. RESULTS: A total of 739 patients were included. Age range at diagnosis was 18 to 49 years; median age was 44 years. Five hundred thirty patients were between the ages of 40 and 49, 167 were between the ages of 30 and 39, 40 were between the ages of 20 and 29, and 2 were under 20. Two hundred thirty-one patients (32%) had a family history of colorectal cancer. The anatomic distribution of the cancers was: 485 rectum (65%), 107 sigmoid colon (15%), 19 descending colon (3%), and 128 right colon and transverse colon (17%). Therefore, 83% of the tumors were theoretically within the range of flexible sigmoidoscopy. LIMITATIONS: Referral bias favors rectal cancer. CONCLUSION: The combination of an increasing incidence of colorectal cancer in those under 50 years of age and the predominance of left-sided cancer suggests that screening by flexible sigmoidoscopy starting at age 40 in average-risk individuals may prevent cancer by finding asymptomatic lesions. See Video Abstract at http://links.lww.com/DCR/A579.