The previous recommendation of yearly mammogram was not based on evidence of effectiveness, it was a guess made under conditions of ignorance about the actual effectiveness of mammograms.
When evaluating the sort of recommendation you have to keep in mind that "more" or "more frequently" does not necessarily equal better; to give an extreme example if we recommended weekly mammograms cancers would certainly be detected earlier, but only at the cost of radically increased radiation exposures which would likely substantially raise cancer rates.
So the question is, what is the most effective schedule?
As the evidence is studied, we're starting to base such recommendations on actual studies of effectiveness, and it turns out that the benefit of yearly mammograms are outweighed by some of the costs. And there's nothing surprising about this: if you think about it it's highly unlikely that the 12 month guess made under conditions of ignorance would turn out on the basis of pure blind luck to be ideal.
Such decisions really are cost-benefit decisions, and as more (and more accurate) information becomes available we will probably be hearing many more such "unintuitive" recommendations for changes in diagnostic and treatment procedures.him
I don’t have a problem with the interval, but the suggestion that the procedure is not needed in those under 50? What about all the women that develop the cancer in their 30s and 40s?