IT'S COSMETICS, NOT MEDICINE:

The results were sobering, as H. Gilbert Welch, a physician at Dartmouth and the study's lead author, explains in this short video. The idea behind cancer screening is that it saves lives by identifying cancers when they are more treatable -- i.e., earlier, when they are smaller. If it works, then we should see a rise in the number of small tumors being detected and a commensurate drop in the number of large cancers, as treating the small cancers would eliminate them before they become big ones, in the same way that picking small zucchini from your garden prevents you from developing humongous ones. But the new study found that although the incidence of cancers smaller than 2 centimeters rose quite dramatically after widespread mammography was introduced, by 162 cases per 100,000 women, the incidence of larger tumors fell by a much smaller amount -- only 30 cases of cancer per 100,000 women. [...]

Most importantly, the incidence of metastatic cancer, which is the type that causes most deaths, was flat. Welch said that means that screening finds a lot of small cancers that would never have killed anyone.

Screening did result in more cancers being detected, he said, but the data suggests that only about 30 of the 162 additional small tumors per 100,000 women that screening mammograms found would ever have progressed to a dangerous stage. That means that 132, or 81 percent, of the 162 extra tumors detected represented "overdiagnosis" -- the discovery and treatment of tumors that were never destined to harm.

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