Thyroid cancer surge puzzles experts as global cases rise faster than other cancers

Thyroid cancer surge puzzles experts as global cases rise faster than other cancers

Thyroid cancer incidence has climbed more rapidly in the U.S. and other regions than any other malignancy, defying broader cancer trends. While often treatable, the disease's accelerating spread-tripling in U.S. men and women between 1980 and 2016-has left researchers searching for explanations beyond improved diagnostics.

The thyroid's role and cancer's rise

The thyroid, a small gland at the base of the neck, regulates critical functions like heart rate, metabolism, and body temperature. Cancer develops when its cells grow uncontrollably, forming tumors that may spread. Data from the U.S. Surveillance, Epidemiology, and End Results (SEER) program shows incidence soared from 2.39 to 7.54 per 100,000 men and 6.15 to 21.28 per 100,000 women over 36 years.

"Thyroid cancer remains one of the few cancers rising despite medical advances," notes Sanziana Roman, an endocrine surgeon at the University of California, San Francisco.

Diagnostic advances: A double-edged sword

Early theories linked radiation exposure-like the 1986 Chernobyl disaster-to thyroid cancer spikes. However, no U.S. nuclear events coincided with the surge. Instead, experts point to thyroid ultrasonography (1980s) and fine-needle aspiration biopsies (1990s), which detected tiny, previously undetectable tumors.

"Doctors could now identify small papillary thyroid cancers that wouldn't have been felt by hand," explains Cari Kitahara, a National Cancer Institute epidemiologist. South Korea's screening program saw cases skyrocket-then decline when scaled back-supporting the overdiagnosis hypothesis.

"These patterns suggest overdiagnosis of cancers unlikely to cause harm if undetected."

Cari Kitahara, National Cancer Institute

Treatment shifts and lingering risks

Most small thyroid cancers grow slowly and respond well to treatment. Yet overdiagnosis led to unnecessary surgeries (e.g., full thyroid removal) and radioactive iodine therapy, risking vocal cord damage or secondary cancers. Recent guidelines now favor partial removal or monitoring for low-risk cases.

By 2022, U.S. incidence stabilized at ~14.1 cases per 100,000, per SEER data. But some researchers argue diagnostics alone can't explain the full rise.

Beyond overdiagnosis: Obesity and environmental factors

Studies reveal thyroid cancer rising even in regions with limited screening, including middle-income countries. Riccardo Vigneri of the University of Catania notes larger, advanced tumors are also increasing-suggesting a mix of detection bias and true incidence growth.

Mortality rates, though low (~0.5 per 100,000), haven't dropped as expected. A 2020 California study found rising diagnoses and deaths across tumor sizes, hinting at deeper causes.

Obesity emerges as a key suspect. High BMI correlates with a 50%+ higher thyroid cancer risk and more aggressive tumors. "Higher BMI links to worse outcomes, not just detection bias," Kitahara says. Potential mechanisms include inflammation, insulin resistance, and thyroid dysfunction.

Other culprits under investigation

• Endocrine disruptors: Chemicals like PFOA/PFOS in household products may interfere with hormones, though evidence remains mixed.
• Trace elements: Volcanic regions (e.g., island nations) show high thyroid cancer rates, possibly tied to zinc, cadmium, or vanadium exposure-but robust studies are lacking.
• Medical radiation: Rising CT/X-ray scans, especially in children, may contribute. One study estimates 3,500 annual U.S. thyroid cancers linked to CT scan radiation.

A multifactorial mystery

Roman emphasizes the likely interplay of "environmental, metabolic, dietary, and hormonal influences," compounded by genetic susceptibility. As research continues, experts urge balanced screening and treatment to avoid overdiagnosis while addressing modifiable risks like obesity.