Some cancers found during routine screening might never hurt you — they grow so slowly that you’d die of something else before they ever became a problem.

In South Korea, more people got thyroid cancer diagnoses after doctors started scanning for tiny lumps—but death rates didn’t go up. This means most of those lumps were harmless and would never have hurt anyone, proving that screening often finds cancers that don’t need treatment.

This study found that many people have tiny thyroid cancers that never caused them any problems — even when they lived to old age. That means if these cancers were found by screening, they probably didn’t need to be treated.

This study says that when men get screened for prostate cancer with a PSA test, many of the cancers found are so slow-growing they’d never hurt the person—even if left untreated. That supports the idea that not all cancers found by screening are dangerous.

This study looked at whether some breast cancers found by screening would never hurt you even if left alone — and found that yes, some probably are harmless, but it’s hard to say exactly how many.