Study Finds High Overdiagnosis Rates for Thyroid Cancer Worldwide

Thyroid cancer rates have skyrocketed globally since the 1980s, but now researchers suspect that has largely been the result of a worldwide trend toward overdiagnosis, which may have caused many patients to receive unnecessary cancer treatments.

In findings published in the November 2024 issue of The Lancet Diabetes & Endocrinology, researchers indicate that the increase in thyroid cancer diagnoses over the last several decades may not have been due to an actual rise in incidences of the cancer, but were likely due to increased screening, creating a public health challenge that needs to be addressed.

The thyroid is a butterfly-shaped gland at the base of the neck, which produces hormones that regulate a large number of the body’s functions, including metabolism, heart rate, body temperature, muscle contractions, bone health and energy production.

The causes of thyroid cancer are not well understood, but it is thought to involve a combination of genetic and environmental factors. Thyroid cancer is usually diagnosed when a person finds a lump in the neck, or a nodule is flagged on an ultrasound or CT scan, and a biopsy of the nodule is done to confirm if it is cancerous or benign.

Once cancer is confirmed patients may undergo a combination of surgery, radioactive iodine, radiation, chemotherapy and hormone therapy as treatment. However, this new research suggests that many of those treatments may not be necessary.

In the study, a group of Chinese researchers, led by Dr. Mengmeng Li, focused on determining the incidence of thyroid cancer around the world, due to what appeared to be an increase over time. They used data from the International Agency for Research on Cancer (IARC) Global Cancer Observatory database, as well as death rate data from the World Health Organization (WHO) from 1980 to 2022. They also used population-based registries across five continents, including 385 registries in 63 countries.

The data indicates rates of thyroid cancer increased from 1980 to 2017 for most countries around the world. The highest rates of thyroid cancer were seen in South Korea, Cyprus, Ecuador, China and Türkiye. Researchers said the increase continued until the early 2010s.

The lowest rates of thyroid cancer for women were 10 per 100,000 people in the 1980s, but by 2012 that rate had reached 101 cases per 100,000 people. Cases also increased among men. Those ranged from 2.7 per 100,000 people in the 1980s to 23.5 per 100,000 people by 2012.

The data indicated from 2013 to 2017, papillary thyroid cancer was the main contributor to the increase in thyroid cancer rates. However, death rates from thyroid cancer were much lower with one to two deaths per 100,000 cases remaining consistent throughout the study period.

Thyroid Cancer Overdiagnosis

By 2010, many countries began to see a decrease in thyroid cancer rates, especially the United States, South Korea, Canada, Israel, France, Italy, Austria and Ireland. As a result, the research team concluded that more than 76% of cases of thyroid cancer were overdiagnosed in recent years, explaining the disparity between rates of diagnosis and death.

They determined that more than 85% of thyroid cancer cases diagnosed in Cyprus, China, South Korea and Türkiye were overdiagnosed. However, countries like Uganda, Zimbabwe and Trinidad and Tobago did not experience similar rates of overdiagnosis.

Overdiagnosis of cancer often involves treatment of benign tumors or other harmless factors, as if they were aggressive and threatened the life and health of the patient. This leads to unnecessary cancer treatments, which can be harsh on the body and often involve adverse health effects.

Improvements in medical screening over the past 40 years have helped to catch cancers at earlier stages, which increases the likelihood of survival for the patient. However, an increase in screening and diagnostic tools can also lead to an increase in the diagnosis of non-threatening and slow-growing cancers, such as some thyroid cancers.

For example, one study published in 2020 by the University of Michigan Rogel Cancer Center found that one-third of thyroid ultrasounds may be unnecessary and will simply catch non-threatening types of thyroid cancer.

Researchers said the overdiagnosis of thyroid cancers is a global health challenge that must be addressed with improved screening and diagnostic tools, so low-risk cancers aren’t diagnosed as more serious malignancies.