There’s no question that tests to detect cancer before it causes any problems can save lives. But such tests can also cause harm through overdiagnosis and overtreatment. A study published yesterday in JAMA Internal Medicine indicates that the majority of people aren’t informed by their doctors that early warning cancer tests may detect slow-growing, or no-growing, cancers that will never cause symptoms or affect health. Undergoing surgery, chemotherapy, or radiation for such cancers provides no benefits and definite harms. The researchers found that only 9.5% of people were informed by their doctors of the risk of overdiagnosis and possible overtreatment. Compare that to 80% who said they wanted to be informed of the possible harms of screening before having a screening test. Informing patients about the risks of screening isn’t easy to do in a brief office visit. It’s complicated information. And the researchers suggest that many doctors don’t have a good grip on relative benefits and harms of screening.