21 November 2012

On objectivity

Now, I'm not a radiologist, oncologist or an epidemiologist. So I am not claiming any expert opinion of the science, but I was not surprised to see yet another major article released regarding the value of early detection of breast cancer via screening mammography -- it tends to detect a lot more early cancers, but doesn't seem to reduce the number of advanced cancers.

From today's NEJM:

The introduction of screening mammography in the United States has been associated with a doubling in the number of cases of early-stage breast cancer that are detected each year, from 112 to 234 cases per 100,000 women — an absolute increase of 122 cases per 100,000 women. Concomitantly, the rate at which women present with late-stage cancer has decreased by 8%, from 102 to 94 cases per 100,000 women — an absolute decrease of 8 cases per 100,000 women. With the assumption of a constant underlying disease burden, only 8 of the 122 additional early-stage cancers diagnosed were expected to progress to advanced disease. ... breast cancer was overdiagnosed (i.e., tumors were detected on screening that would never have led to clinical symptoms) in 1.3 million U.S. women in the past 30 years. We estimated that in 2008, breast cancer was overdiagnosed in more than 70,000 women; this accounted for 31% of all breast cancers diagnosed.
This is not a new finding at all. Numerous previous studies have been published questioning the value of rountine mammography screening in younger women, and a major controversy was ignited a few years ago when the experts at the USPSTF finally recommended that women under the age of 50 not be routinely screened by mammograms.

As I disclaim above, I do not have a vested interest or a strong opinion on this, though I do have a bias towards accepting the conclusion as the body of science accumulates. But one thing that I noted in the media coverage of this newest study was this statement which was almost universally cited:
The American College of Radiology issued a statement saying the report was "deeply flawed and misleading"
While I understand that journalists should try to present both sides of an issue, especially one which is so controversial and emotionally charged, maybe an organization which has such a strong, vested, economic interest in the value of mammography might not be the most credible source to turn to for an expert opinion? As Upton Sinclair famously said, "It is difficult to get a man to understand something, when his salary depends upon his not understanding it!"


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