Impact of Screening on Early- and Late-Stage Colorectal Cancers

At the 2013 meeting of the American Society of Clinical Oncology (ASCO), Daniel Xiao Yang, a medical student at Yale University, New Haven, Connecticut, discussed his poster (ASCO abstract 1522), “Changes in Early and Late Stage Colorectal Cancer Incidence During the Era of Screening: 1976–2009,” which clearly shows the health benefit of screening colonoscopy. Mr. Yang’s coauthors on the study are Cary P. Gross, MD, Pamela Soulos, MPH, and James B. Yu, MD, all from Yale School of Medicine and from Yale Cancer Center and the Cancer Outcomes Public Policy and Effectiveness Research (COPPER) Center at Yale.

As the authors point out in their background to the study, while colorectal cancer screening via colonoscopy in the United States commonly is performed on adults 50 years of age and older, with the goal of earlier detection and a better chance of cure, the estimated number of colorectal cancers prevented by colorectal cancer screening in the United States is not well known.

Their correlation and assessment of information from the SEER (Surveillance and Epidemiology End Results) database (for cancer incidence) and from the National Health Interview Survey (for colonoscopy utilization) shows the positive impact of colorectal cancer screening on the incidence of both early-stage (in situ or localized at the time of diagnosis) and late-stage (regional or distant staging at diagnosis) colorectal cancer between 1976 and 2009.

The authors used the incidence of colorectal cancer in the United States between 1976 and 1978 as the initial baseline incidence, and found a 0.4% annual increase in colorectal cancer incidence from baseline in the non-screened population. They used this 0.4% annual percentage change to estimate the underlying rate of change in colorectal cancer incidence and assess the impact of colorectal cancer screening on that rate over a 30-year period, in the US population younger than 50 years and age 50 or older (the group that generally underwent colorectal cancer screening).

They found that, from 1976 to 2009, late-stage cancer incidence decreased from 117 to 74 cases per 100,000 people, and early-stage incidence decreased from 77 to 68 cases per 100,000. Correlating this with screening efforts, from 1987 to 2010, screening colonoscopy utilization increased from 27% to 63%. In the period 1976 through 2009, there was a net surplus of 15,825 cases over baseline for early-stage cancers and a net reduction of 565,425 cases from baseline for late-stage cancers, underscoring the benefit of screening colonoscopy.

Mr. Yang discusses his poster in the interview below.

Daniel X. Yang: Hi, my name is Daniel Yang, and I’m a medical student at Yale University.  I’m talking about changes in early and late-stage colorectal cancer, looking back at the data going from 1976 to 2009. And we were looking at the colorectal cancer incidence in the United States, looking at the cancer incidence from the SEER database and correlating that with colonoscopy utilization or colorectal cancer screening rates from the National Health Interview Survey.

And what we found is that, over the last 30 years we saw this marked decline in both the early-stage cancers and the late-stage colorectal cancers. You see the early-stage declining and you also see a more significant decline in the late stage, going from 117 cases back in 1976 per 100,000 people down to 74 cases per 100,000 people in 2009. At the same time, you see this marked increase in colonoscopy utilization, representing increased rates of colorectal cancer screening-you see this clear juxtaposition between this increased screening with this decrease in incidence.

What’s interesting is that we were looking at this in US adults 50 years and older, so people who generally receive screening, but if we look at the same parameters for people who generally did not receive screening in the United States, so, people younger than 50 years, we see almost no change, as you would expect. So, the total cancer incidence remained relatively constant, at 0.4% annual percentage change.

Cancer Network: That’s very interesting because it suggests public efforts at patient education broadly but maybe not increased efforts to educate about hereditary cancers, which would affect a younger population, like Lynch syndrome.

Mr. Yang: Absolutely. That would be very interesting to look at. We were looking at the US population as a whole, without looking specifically at hereditary cancers, but I think that would be absolutely fascinating to look at as a further step in our study.

And here we see, going back [to our study], we found a 0.4% annual percentage change [increase in colorectal cancer incidence from baseline] in the non-screened population, so we used that as an estimate of what is the underlying rate of change in the cancer incidence in the absence of screening. When we looked at the cancer incidence change at baseline level-we took the 1976 rate-and increased it at 0.4% annual percentage change every year, and then we plotted that, and we combined that with the early [colorectal] cancer incidence, we found a difference between the early cancer incidence line and the baseline line, and we summed that difference for every year over the last 30 years. And we saw that, for early-stage [colorectal cancer], there was a net surplus, of about 16,000 cases over the baseline expected cancer rate. And for the late-stage [colorectal cancer], if we look at the same parameters, we see that there was a reduction [in incidence], of about 560,000.

So what this tells us it that, over the last 3 decades, we see a reduction of almost 550,000 cases of cancer that’s associated with colorectal cancer screening.

Cancer Network: Great, very interesting study. Thank you very much.

Mr. Yang: You’re welcome.