Breast cancer and stroke screening stories that deserve careful attention

Two screening test stories – both of which discuss the work of the US Preventive Services Task Force – that deserve much more analysis than I can afford to give right now. This is a casualty of our current funding plight.  As it is, in the first four hours that I’ve been at the computer today, I’ve received at least five requests from readers to review/analyze/comment on things they’ve sent me.  I can’t get to it all. *

    • ADDENDUM on September 10:  A “Research News” piece in the BMJ reports:
      • “Klim McPherson, visiting professor of public health epidemiology at the University of Oxford, dismissed the research. He said, “These authors tell us that randomised controlled trials underestimate the effects of mammography, but don’t say why. Nor do they say anything about overdiagnosis, overtreatment, lead time bias, and length biased sampling. Finding a tumour early is necessary but not sufficient for screening to save lives. It might just mean that screen detected cancers have longer to go in their natural history with treatment than otherwise and hence survival from diagnosis could be longer without any benefit.”

        McPherson told the BMJ, “Screen detected cancers are necessarily slower on average than non-screening detected cancers because they thus stand a better chance of being detected at any one mammogram in their (longer) pre-clinical period. That is precisely why screening is evaluated with randomised controlled trials, being the only way to eliminate these biases in the relevant comparison. These [failure] analyses are subject to serious unknown bias—in spite of their obvious appeal.”

        Karsten Jørgensen, a researcher at the Nordic Cochrane Centre in Copenhagen, told the BMJ, “We already know that breast cancer deaths are more common in non-attenders to breast screening. We also know that much of this difference is due to selection bias and are not an effect of screening—a factor this study does not explore. Health-concerned women in high socio-economic groups with a strong network are more compliant with treatment and are also more likely to attend screening. This is what makes case-control studies problematic in breast screening.”

        He added, “This study also disregards that overdiagnosis of invasive breast cancers in screened women will substantially affect their analyses. The largest reductions in breast cancer mortality, 30-50%, have been seen among women too young to be screened and are a major achievement of modern breast cancer treatment. This has substantially reduced the potential absolute benefit of breast screening for younger women, a group where older randomised trials already showed a small effect, probably because these women often have fast growing tumours, which are more difficult to catch with screening (length bias).”

  • A Wall Street Journal column, “A Common Test to Screen for Stroke Risk Is Under Review: Health panel takes a new look at carotid-artery ultrasounds, which can produce false positive results.” The piece discusses how the Life Line Screening company continues to promote such screening, although “the use of carotid-artery screening has been highly controversial, in large part because studies show the ultrasound tests have only moderate sensitivity and can produce false-positive results. Follow-up often leads to more sensitive tests that can actually have adverse effects on the patient; in some cases, people with false-positive test results may end up getting unnecessary invasive surgery, according to the U.S. Preventive Services Task Force, which issued a recommendation in 2007 against screening patients without symptoms of disease. The task force is now reviewing that recommendation as part of its efforts to consider new evidence every five years, according to Michael LeFevre, co-vice chairman of the task force and a professor at the University of Missouri School of Medicine. Dr. LeFevre says the concern isn’t that the ultrasound itself is dangerous, but rather that it can lead to “a cascade of events” that “do more harm than good.” (Note:  This is a pre-emptive warning to those inclined to participate in an Astroturf comment campaign on behalf of Life Line Screening.  Write to the Wall Street Journal, not me.  They published the column. I didn’t.  They have a huge staff.  I don’t. I don’t have time to moderate back-and-forth comments about the pros and cons of Life Line Screening’s business model.)

* In the past, with foundation funding, we would have been all over these stories with independent, expert analysis. I could have turned to a terrific team of reviewers. Currently I am keeping this site going by myself and cannot devote the time to the kind of analysis that’s required.  Rather than post a half-hearted analysis, I simply bring these to your attention and await the day when we can return to our former robust reporting on such issues.


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