Sometimes, doctors treat small, slow-growing lung growths like they’re dangerous, even though they’re not likely to hurt you—leading to unnecessary surgeries or chemo that might do more harm than good.

This study says that some lung cancers found in scans grow so slowly they’d never hurt you, but doctors sometimes treat them like dangerous cancers with surgery or chemo—unnecessarily. The study agrees this is a problem and suggests a better way to tell which cancers are harmless.