The Hubris of Screening for Disease -- Again

One thing you learn from years of working in the hospital is the utter unfairness of disease. You see people doing everything right—diet and exercise—and still succumb to some often obscure noncardiac cause of death. There are thousands of fatal diseases that can take you out. It doesn’t even have to be disease; a car wreck can be fatal. This fact has always made me see screening for disease in asymptomatic people as foolish. In other words, even if a screening test had perfect sensitivity and specificity it would still fail to prolong life. A recent observational study of more than 90,000 US veterans’ only strengthens this take. The specific study question obscures the larger message of competing causes of death—AKA other shit that can kill you. The UCSD-led team focused on the risk of colorectal cancer (CRC) and all-cause mortality in people age 75 years or older who had (or did not have) an adenoma on a previous colonoscopy. Current guidelines recommend stopping screening colonoscopy at age 75, but what if the patient at age 72 had an adenoma? [Quick background: adenomas are polyps — abnormal growths projecting from the mucosal lining of the colon or rectum that have undergone dysplastic (pre-cancerous) changes. They matter because colorectal cancer almost universally follows the adenoma → carcinoma sequence. This process takes years.] Using the VA database the authors made two groups of patients: those with and without an adenoma on colonoscopy before age 75. The main outcome measures were the incidence of CRC, CRC death and non-CRC death and all-cause death. Of the 91,000 patients (mean age 71), 28% had an adenoma and 72% did not have one. At 10-year follow-up, the cumulative incidence of CRC was 1.1% in those with adenoma vs 0.7% in those without adenoma. At 10-year follow-up, the cumulative incidence of CRC death was 0.5% in those with adenoma vs 0.4% in those without adenoma. The cumulative incidence of non-CRC death ranged from 46.9% to 48.4% at 10 years. I’ve attached a screenshot from the paper. Look at the red rectangles. In the 25,000 pts with adenomas before age 75, there were 45 patients who died of colorectal cancer over the next decade. But there were 4,408 patients who died of something else. Many of you may ask about higher risk adenomas. There was no difference in future cumulative CRC risk. The authors spend a lot of gentle words in their discussion explaining how it is reasonable to stop doing colonoscopy after age 75—even when there is an adenoma. I would look at the larger picture. From the Table above, the 10-year risk of dying from colorectal cancer at age 71 (the average age of this study) was 0.5% even if you had an adenoma. The risk of dying from something other than colon cancer was 48%. Now do fractions: 48% divided by 0.5% = you are 96 times more likely to die of something else. Not 50% higher; not double the risk, but 96 times more likely. This study was done in 71-year-olds and we all know that death comes to us all, and the older we get, the higher the odds of all diseases. So a screening advocate might argue that we should keep screening but do it in younger people. My rebuttal would be what do you think the ratio of CRC death to other death looks like at age 60 or age 50 years? Well… we can look at the NordICC trial of screening colonoscopy published in NEJM in 2022. In the 56,000 individuals in the control arm of that study, 157 people died of colorectal cancer (0.31% over 10-years) vs 6079 people who died of any cause (11%). Younger people therefore only have a 36x greater risk of dying from non-colorectal cancer. (By the way, the ratio was the same in the screening arm: 11% vs 0.28%). If you have blood from the rectum, or a strong family history of colon cancer, you should be checked. But if you are a regular person, how does it make sense to look for one disease when you are 36-90 times more likely to die from something else. I am asking. Tell me.