Examining the increasing incidence of colorectal cancer in younger adults Public Deposited

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  • March 20, 2019
  • Murphy, Caitlin
    • Affiliation: Gillings School of Global Public Health, Department of Epidemiology
  • The overall incidence of colorectal cancer (CRC) has declined in the U.S., but the incidence of CRC in younger adults (age <50) is rapidly increasing. The underlying mechanisms that have contributed to this increase are poorly understood. This dissertation project sought to: 1) describe the demographic, clinicopathologic, and socioeconomic characteristics and treatment patterns of younger stages II and II CRC patients; 2) estimate the contribution of age, time period, and birth cohort to the increasing incidence of young-onset CRC; and 3) determine patterns of colonoscopy use in younger adults. Several population-based data sources were leveraged to examine reasons for the increasing incidence of young-onset CRC. The National Cancer Institute’s Patterns of Care studies were used to describe differences in the characteristics of stages II and III CRC patients by age at diagnosis. Hierarchical Poisson models were used to estimate the independent contribution of age, time period, and birth cohort on increases in the incidence of young-onset CRC. Incidence rates were derived from the Surveillance, Epidemiology, and End Results program of cancer registries. The prevalence of CRC risk factors, including obesity, physical inactivity, and smoking, were also described across time period and birth cohort using data from national surveys. Lastly, MarketScan Commercial Claims and Encounters Data, an employer-based claims database, was used to characterize patterns of colonoscopy use in younger adults. There were differences in the distribution of young-onset CRC by race/ethnicity. A higher proportion of black and Hispanic patients were diagnosed at a younger age compared to whites. Results of the age-period-cohort analysis showed a significant age and birth cohort effect in both younger and older populations, but the effect of time period was only observed among older ages. The prevalence of obesity generally increased across both time period and birth cohort, while smoking prevalence declined. Trends in physical inactivity remained relatively constant. Colonoscopy use among younger adults increased across sex, age, and geographic region from 2001 to 2009 and decreased through 2013. This study provides strong support for different mechanisms involved in the development of CRC across the life course. The factors responsible for increases in young-onset CRC, albeit small on in absolute magnitude, remain unknown.
Date of publication
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Rights statement
  • In Copyright
  • Sanoff, Hanna
  • Yang, Claire
  • Baron, John
  • Lund, Jennifer
  • Sandler, Robert
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2016

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