Date of Award

January 2017

Document Type


Degree Name

Medical Doctor (MD)



First Advisor

James B. Yu



Daniel X. Yang and James B. Yu, Department of Therapeutic Radiology, Yale School of Medicine, New Haven, CT

Effective cancer screening detects cancer at an earlier and more curable stage, and thus reduces incident late-stage disease. However, in recent years, there has been sustained controversy over the net benefit of cancer screening due to concerns of overdiagnosis and overtreatment. Therefore, we sought to demonstrate the impact of cancer screening efforts at the population level, specifically examining incidence trends in colorectal, cervical, and prostate cancers. We sought to estimate the number of cervical and colorectal cancer cases prevented during an era of widespread screening, and to examine temporal associations between the 2012 United States Preventative Services Task Force (USPSTF) recommendation against PSA screening and emerging trends in metastatic prostate cancer. We hypothesize that screening efforts would be associated with characteristic shifts in cancer incidence: (1) Increased colonoscopy and sigmoidoscopy utilization would drive increased detection of left-sided colorectal cancers; (2) Widespread Pap smear use would be most effective in higher-risk populations; and (3) Decreased PSA screening would lead to increased late-stage disease. Colorectal, cervical, and prostate cancer incidence spanning over three decades from 1973 to 2013 were collected from the Surveillance, Epidemiology, and End Result (SEER) database. Screening utilization trends were collected from the National Cancer Institute Progress Reports, the National Health Interview Survey, and literature review. We demonstrate that widespread colorectal and cervical cancer screening were temporally associated with 236,000 to 550,000 cases of colorectal cancer and 105,000 to 492,000 cases of cervical cancer, respectively, over the past three decades from 1979 to 2009. Over this time period, the incidence of late-stage colorectal cancer decreased from 118 to 74 cases per 100,000 people (p < .001), and the incidence of late-stage cervical cancer decreased from 5.3 to 3.7 cases per 100,000 women (p < .001). Since the 2008 to 2012 pullback in PSA screening, metastatic prostate cancer incidence among United States men age 70 years or older increased from 54.2 per 100,000 men in 2011, to 56.6 per 100,000 men in 2012 and 59.5 per 100,000 men in 2013. Moreover, we address our hypotheses by: (1) Demonstrating a more prominent decrease in left-sided compared to right-sided colorectal cancer incidence; (2) Demonstrating a convergence of race-specific cervical cancer incidence over time; and (3) Characterizing the recent increase in metastatic prostate cancer incidence. Taken together, our studies document the successes of screening efforts as well as underscore the challenges of balancing the benefits of early detection against the risks of overdiagnosis and overtreatment.


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