Posted: February 2, 2017

The death rate from colon cancer is plummeting in the United States.  From 1975 to 2012 the incidence of metastatic disease (which almost inevitably is fatal) has fallen from 50/100,000 to 25, a 50% reduction.  The big question: why??

Several people have weighed in on this but the best review is from Dartmouth, by Gilbert Welch.  Regular readers of these postings may recall that Dr. Stark is not a big fan of Gilbert Welch.  His analysis of what breast cancer treatment — that millions of women get too much treatment — is held is some suspicion in many quarters, not just Stark’s.  His taking on colon cancer is a newer development.  He published his results in the New England Journal of Medicine.

Here is what he found: first of all, even though more people over age 50 are getting screened than ever before the percentage of people screened at appropriate intervals is still much less than 50%.  It would take a remarkable change in the natural history of the disease with screening to result in a 50% reduction in mortality, and Welch isn’t buying this as the sole cause.  He cites improved surgical technique and better and better chemotherapy regimens given to patients found to have lymph node involvement at surgery.  He also believes that the widespread availability of colonoscopy as made this the diagnostic tool of choice in people with ill-defined abdominal symptoms, leading to earlier diagnoses.   He also cites at least the possibility that life-style changes are leading to a lower incidence of colon cancer: less meat consumed; widespread use of antibiotics leading to a change in intestinal flora; and the widespread use of non-steroidal anti-inflammatory drugs, which are believed to slow the development of colon polyps.

So Welch comes to no real conclusion as to why fewer people are dying of colon cancer, but his hypotheses are thought provoking.  It would be very difficult for a clinical trial to tease out these various hypotheses as to importance, but this paper should result in a heightened awareness of the issues.  Welch does not believe his conclusions should lead to a weakening of the efforts to develop effective public policy regarding screening, which he still views as important.   Current recommendations from the US Preventive Services Task Force for screening can be found here.