f1jim wrote: the problems with looking at "survival" statistics. They are almost meaningless since they are all simply dictated by the time of diagnosis...
Our best treatments tend to extend the lives of cancer patients measured in months. And that's the best.
It's hard to swallow but for breast cancer it doesn't matter much when we find it. This appears to be counter intuitive, but it's not.
The nice thing about the H. Gilbert Welch book is it's explanation of all the terms we through out in evaluating procedures. 5 year survival, mortality, lead times, and the big elephant in the room, overdiagnosis. His book will unlock much of the world of studies to anyone that is confused by them. It tells you what the important numbers are in evaluating procedures and pills and which ones to ignore. It was eye opening to me.
f1jim
There are some cancers that are amenable to early treatment and therefore the time of diagnosis does matter. The problem is that mammography can't distinguish those, and finds cancers that are also equally amenable to late treatment, and cancers that are never amenable to treatment, and ... cancers that don't ever need treatment and would never ever cause a problem anyway. And that last number (the number overdiagnosed) is 50% of all "non-palpable" "cancers" found (ones that we wouldn't find anyway in the shower). Which is why it's not just lead time that changes the numbers -- a full 50% of the additional cancers we're counting in the mammography group have an infinite breast cancer survival rate that is being averaged in -- but those women will never die of breast cancer no matter what. And -- a big chunk of that time they want to be spending with their grandkids is instead spent in chemo and radiation and surgery and worry about the big C. AND ... some of them will die from the "treatment" of a problem they don't actually have. But those are all part of the group of women running around saying mammography "saved" them, and the numbers are so high we're all quite likely to know someone who is part of that group of having had needless breast cancer treatment yet thinking they were part of the group that had a cancer that needed to be treated, needed to be treated early and was found and treated early because of mammography.
Oh, and the study we're referring to here was a 25-year study of 89,000 women -- a huge sample size and extremely long-term (five-year survival rates are less meaningful I think). But there are many many more finding basically the same thing.
Screening mammography (mammography in women without any signs or symptoms of possible breast cancer) has been studied in large randomized trials of nearly a half million women. The theoretic basis for the intervention is sound. It is presumed that therapeutic intervention at a point when cancer is visible on a mammogram but not yet palpable in the breast will, for a small number, result in earlier, ultimately life-saving, therapy. Overall mortality rate, however, was not improved in the groups in these studies assigned to receive regular mammograms. When aggregating data from those trials in which randomization was appropriate (resulting in balanced groups), there was also no identifiable reduction in deaths due to breast cancer.
If screening mammography reduces the rate of one type of death, but the overall rate of death is not affected, it is mathematically implied that there is an increase in some cause of death that is offsetting the reduction in breast cancer deaths. Unfortunately, because most massive trials of mammography are simply too large to reliably track every cause of death, it is often difficult to tell with precisions where this increase occurs.
Harms due to breast cancer screening are discussed at length in the Cochrane review, and in more recent analyses.2,3 These include false positives that result in surgical procedures, and emotional distress due to false positives. In addition, despite the lack of identifiable benefit to screening mammography, women in groups assigned to receive mammograms were 20% more likely to undergo mastectomy and 30% more likely to undergo surgery. Finally, if it is true that breast cancer deaths are reduced it has been estimated that for every one patient who avoids death from breast cancer approximately 10 to 20 women are treated unnecessarily as cancer patients, typically receiving surgery, radiation, and chemotherapy.3,4 This additional estimate of harm is not represented in the NNH statistics listed above.
http://www.thennt.com/nnt/screening-mammography-for-reducing-deaths/