The increased use of mammograms to screen for breast cancer has subjected more women to invasive medical treatments but has not saved lives, a new study says. After reviewing cancer registry records from 547 counties across the United States, researchers concluded that the screening tests aren't working as hoped. Instead of preventing deaths by uncovering breast tumors at an early, more curable stage, screening mammograms have mainly found small tumors that would have been harmless if left alone ... researchers reported Monday in the journal JAMA Internal Medicine. Ideally, the counties with more widespread screening would see a payoff in the form of lower rates of breast cancer deaths. Instead, the researchers found "no evident correlation between the extent of screening and 10-year breast cancer mortality," they wrote. The results are sure to be troubling to those who have faith in the idea that if mammograms are good, more mammograms must be better. If that were the case, the researchers should have found lower breast cancer mortality rates in counties where screening was more widespread, according to a commentary that accompanied the study. "Sadly, we are left in a conundrum," the commentary authors wrote. "Women will increasingly approach their physicians with questions and concerns about overdiagnosis, and we have no clear answers to provide."