New medical research has cast doubt on the value of mammograms, the test used to screen for breast cancer. A wide-ranging study in the British Medical Journal involving nearly 90,000 women has found death rates, both from breast cancer and other causes, were the same regardless of whether a woman underwent mammograms or not. In fact, the study found one-in-five women whose cancers were detected by mammograms in the early 1980s were “over diagnosed” and underwent unnecessary treatment for slow-growing cancers that did not pose a threat to life expectancy.