Increasing Incidence of Left-Sided Colorectal Cancer in the Young: Age Is Not the Only Factor.

Background: Recent single-institution studies have shown that colorectal cancer (CRC) in patients < 50 is predominantly left-sided. The aims of this study were to 1 compare the incidence of left-sided CRC in patients under and over 50, 2 investigate this trend over time, and 3 examine whether racial differences exist in the anatomical distribution of CRC.

Methods: We used the Nationwide Inpatient Sample to identify all patients with colon or rectal cancer who underwent a resection from 2000 to 2014. Logistic regression models were used to determine the odds of a patient having a left-sided CRC based on age and race.

Results: A total of 1,547,589 patients underwent resection, with a mean age of 68.6. Overall, 65.1% of patients < 50 had a left-sided CRC compared with 47.2% of patients ≥ 50 (OR = 2.1; 95% CI 2.0, 2.1). The difference was greater as patients became older with 39.9% of patients > 70 having a left-sided CRC (< 50 vs ≥ 70; OR = 2.8; 95% CI 2.7, 2.9). The incidence of CRC in those under 50 increased over the study period due to an increase in left-sided tumors. The distribution of CRC varied with race, with African-Americans having a lower odds for left-sided CRC (OR = 0.89; 95% CI 0.87, 0.91) and Asians/Pacific Islanders having a higher odds (OR = 1.8; 95% CI 1.7, 1.9).

Conclusion: In the < 50 age group, the incidence of CRC is increasing, with majority of these tumors left-sided. Tumor location varies with both age and race.