Getting everyone screened for thyroid cancer finds a lot of harmless lumps that would never hurt you, so more people are told they have cancer—but it doesn’t save any lives.

This study found that checking people’s thyroids with ultrasound finds lots of small cancers, but doesn’t help people live longer — meaning many of those cancers were harmless and didn’t need to be found or treated.

Doctors in South Korea started using ultrasounds to check healthy people for thyroid cancer, and they found way more tiny, harmless tumors — but people weren’t dying less. The study says this means we’re just finding cancers that would never hurt anyone.

In South Korea, more people got thyroid cancer diagnoses after doctors started using ultrasounds to check healthy people—but the cancer cases found were tiny and wouldn’t have hurt anyone. The study says screening found these harmless lumps, not life-threatening ones, and didn’t stop anyone from dying of thyroid cancer.

This study found that many people have tiny, harmless thyroid cancers that never cause problems — even in old age. This helps explain why more thyroid cancer diagnoses from screening don’t lead to fewer deaths: we’re just finding cancers that wouldn’t have hurt anyone.

In Korea, more people were tested for thyroid cancer, so more cases were found — but the number of people dying from it didn’t go down. That means many of those extra diagnoses were for cancers that wouldn’t have hurt anyone, proving that too much screening can find harmless lumps.