The American Cancer Society has long supported most cancer screening, but is now warning that screening for breast, prostate and some other cancers can create a risk of overtreating smaller cancers, while missing others that are deadly. “I’m admitting that American medicine has overpromised when it comes to screening. The advantages to screening have been exaggerated,” said Dr. Otis Brawley, chief medical officer of the cancer society, adding that he doesn’t “want people to panic.” The cancer society, one of the largest voluntary health agencies in the U.S., doesn’t advocate prostate testing for all men; researchers point out the test hasn’t been shown to prevent prostate cancer deaths. But there’s been less debate around mammograms, which have been shown in many studies to reduce the death rate from breast cancer by up to 20 per cent. In an analysis published Wednesday, researchers report a 40 per cent increase in breast cancer diagnoses and a near doubling of early stage cancers, but just a 10 per cent decline in cancers that spread from the breast to the lymph nodes or elsewhere. The situation with prostate cancer is similar, according to researchers, who say that, if screening for breast and prostate cancer lived up to their claims, cancers that were once found late would now be found early, and could be cured. Some worry the research could confuse the public and turn them away from screening. “I am concerned that the complex view of a changing landscape will be distilled by the public into yet another ‘screening does not work’ headline,” Dr. Begg said. “The fact that population screening is no panacea does not mean that it is useless,” Colin Begg, a biostatistician at Memorial Sloan-Kettering Cancer Center in New York, told the Times.