Widespread screening for thyroid cancer increases the diagnosis rates of thyroid cancer without reducing mortality, because screening detects indolent, non-life-threatening tumors that would not have caused death if left undiagnosed.

Study: Association of Screening by Thyroid Ultrasonography with Mortality in Thyroid Cancer: A Case–Control Study Using Data from Two National Surveys

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.

Study: Prevalence of Subclinical Papillary Thyroid Cancer by Age: Meta-analysis of Autopsy Studies.

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.

Study: Association between screening and the thyroid cancer “epidemic” in South Korea: evidence from a nationwide study

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.

Study: Association between screening and the thyroid cancer “epidemic” in South Korea: evidence from a nationwide study

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.