Why are there increasing cases of thyroid cancer worldwide?

I. A Revolution in Diagnostic Technology: From "Invisible" to "Detecting Lesions as Small as 2 Millimeters"

"The explosive growth in the incidence of thyroid cancer is 80% attributable to innovations in diagnostic technology." This viewpoint, expressed by Guo Xiaohui, Chief Physician of the Department of Endocrinology at Peking University First Hospital, reflects a global consensus in the medical community. Before the widespread adoption of ultrasound technology, thyroid cancer was detected entirely by touch—it was only possible to detect tumors that grew to over 1 centimeter, forming a palpable mass in the neck. Now, high-resolution ultrasound has an accuracy of 0.1 millimeters, clearly displaying tiny nodules of 2-3 millimeters, and even distinguishing subtle features such as nodule boundaries and calcifications. The case of South Korea is highly representative. After South Korea included thyroid ultrasound in its nationwide health check-up program in 1999, the incidence of thyroid cancer skyrocketed from 4 cases per 100,000 people to 60 cases, a 15-fold increase in 15 years, but the mortality rate remained stable at around 0.5 cases per 100,000 people. “This means that the vast majority of new cases are extremely slow-growing papillary microcarcinomas, which may never progress and will not threaten life,” explained Kim Min-cheol, an epidemiologist at the National Cancer Center of Korea. These “lazy cancers” were previously only considered benign nodules and may even remain undetected throughout a person’s life. The situation in China is even more pronounced. With the physical examination coverage rate increasing from less than 10% in 2000 to 68% in 2024, the proportion of papillary microcarcinomas (≤1cm in diameter) in new thyroid cancer cases increased from 32% to 76%. More advanced diagnostic technologies are continuously increasing the detection rate: The latest research from the Chinese Anti-Cancer Association shows that the ThyMet detection technology based on cfDNA methylation has a diagnostic specificity of 94.4% for papillary microcarcinomas, far exceeding the 22.2% of traditional ultrasound, and the diagnostic accuracy after combining with ultrasound is as high as 92.3%. "It's like we suddenly have a microscope, allowing us to see 'enemies' we couldn't see before," said Wang Lühua, director of the Department of Head and Neck Surgery at the Cancer Hospital of the Chinese Academy of Medical Sciences. He likened this "detection equals diagnosis" model to transforming thyroid cancer from a "rare disease" into a "common disease." However, he emphasized that advancements in diagnostic technology have not changed the true incidence of thyroid cancer; they have merely brought this "silent cancer" to the surface.

II. Environmental Hazards: The "Invisible Attack" of Radiation and Chemicals While diagnostic technology is the primary cause, the medical community generally believes that the increase in some thyroid cancer subtypes has a "real component," and environmental factors are a significant driving force. The thyroid gland is one of the most sensitive endocrine organs in the human body. Long-term exposure to ionizing radiation and chemical pollutants significantly increases the risk of cancer. The dangers of ionizing radiation have long been proven. After the Chernobyl nuclear accident in 1986, the incidence of thyroid cancer in children in the surrounding areas increased 60 times within 10 years; after the Fukushima nuclear accident in 2011, thyroid cancer screening in Japan found that the incidence rate in people under 30 years old was three times the national average. "The thyroid gland is particularly sensitive to radiation during childhood; even low-dose exposure can induce gene mutations," pointed out Tan Dong, chief physician of the Department of Neurology at Qilu Hospital of Shandong University. Medical radiation should not be ignored either; frequent neck CT scans and X-rays can increase the cumulative radiation dose to the thyroid gland, which may induce cancer in the long term. An even more insidious threat comes from endocrine disruptors in the environment. A 2024 study published in the journal *Environmental Health Perspectives* showed that chemicals such as bisphenol A (BPA) and polychlorinated biphenyls (PCBs) can interfere with thyroid hormone secretion, leading to abnormal proliferation of thyroid cells. These substances are widely found in plastic containers, cosmetics, and pesticide residues, entering the human body through food and respiration. "We tested the blood of 100 thyroid cancer patients, and 83 of them tested positive for excessive levels of BPA, at concentrations 2.3 times higher than those in healthy individuals," revealed Emily Carter, a researcher at the National Institute of Environmental Health Sciences. Air pollution has also become a new risk factor. A 2023 study by the Chinese Center for Disease Control and Prevention found that for every 10 μg/m³ increase in PM2.5 concentration, the risk of thyroid cancer increases by 8%. "Heavy metal particles in PM2.5 can deposit in thyroid tissue, causing chronic inflammation, and long-term stimulation can lead to cell carcinogenesis," explained the study's lead researcher.

III. Lifestyle and Genetics: The Trio of Obesity, Stress, and Genes Beyond diagnostic techniques and environmental factors, changes in modern lifestyles are reshaping the incidence profile of thyroid cancer. Epidemiological data shows that obese individuals have a 45% higher risk of thyroid cancer than those of normal weight, and the incidence rate in women is three times that of men, which is closely related to fluctuations in hormone levels. "Obesity leads to insulin resistance, which in turn stimulates the secretion of thyroid hormones. Excessive hormones promote thyroid cell proliferation, increasing the probability of cancer," points out Jiang Fusong, Chief Physician of the Department of Endocrinology and Metabolism at Shanghai Sixth People's Hospital. He notes that the global obesity rate rose from 4.8% in 1975 to 13.1% in 2024, a figure that closely matches the growth curve of thyroid cancer. Furthermore, factors such as prolonged sleep deprivation and high stress levels can lead to endocrine disorders, reducing the body's immunity and providing an opportunity for cancer cell proliferation. Genetic factors also play a significant role in the development of thyroid cancer. Studies have found that carriers of RET gene mutations have a 50 times higher risk of developing thyroid cancer than the general population, while the detection rate of BRAF gene mutations in papillary carcinoma is as high as 60%. "If there is a family history of thyroid cancer, an individual's risk increases by 3-5 times," warns Liu Zhongqi, chief physician of the Department of Otolaryngology-Head and Neck Surgery at Peking University Third Hospital. He advises that this group should begin thyroid screening earlier. It is noteworthy that the high incidence rate in women is closely related to estrogen levels. Estrogen receptors exist in thyroid tissue, and estrogen promotes thyroid cell growth, which explains why thyroid cancer is more prevalent in women of childbearing age and menopausal women. "Hormonal fluctuations caused by factors such as pregnancy and the use of birth control pills can stimulate the growth of thyroid nodules, and some benign nodules may transform into malignant ones," adds Guo Xiaohui.

IV. Iodine Intake Controversy: Excess or Deficiency? Iodine is an essential element for the synthesis of thyroid hormones, but the relationship between its intake and thyroid cancer has been a subject of decades-long debate globally. Since China implemented a universal iodine supplementation policy in 1994, the incidence of thyroid cancer has continued to rise, leading to widespread claims that "excessive iodine supplementation causes cancer."

"Currently, there is no clear evidence that excessive iodine supplementation directly causes thyroid cancer, but an imbalance in iodine nutrition does increase the risk," explained Jiang Fusong. Iodine deficiency can lead to compensatory hyperplasia of the thyroid gland, forming nodules, while long-term excessive iodine supplementation may induce autoimmune thyroiditis, both of which are risk factors for thyroid cancer. Data from the Chinese Center for Disease Control and Prevention shows that the average iodine intake of Chinese residents increased from 80 μg/day in 1994 to 230 μg/day in 2024. Although this does not exceed the WHO recommended upper limit (300 μg/day), excessive iodine supplementation exists in some areas. Different types of thyroid cancer show significant differences in their sensitivity to iodine. Papillary carcinoma is more prevalent in high-iodine areas, while follicular carcinoma has a higher incidence in iodine-deficient areas. "This shows that iodine intake needs to be maintained at an appropriate level, neither insufficient nor excessive," said Yang Xiaoguang, chairman of the Trace Elements Branch of the Chinese Nutrition Society. He suggested that residents should adjust their diet according to the iodine nutrition status of their area. Coastal areas can appropriately reduce their intake of iodized salt, while inland areas need to ensure adequate supplementation.

V. The Overdiagnosis Controversy: Reflections on "Detection and Treatment" Behind the surge in cases, a debate about "overdiagnosis" versus "overtreatment" is brewing in the global medical community. Data shows that the global 5-year survival rate for thyroid cancer has reached 98%, with the 10-year survival rate for papillary microcarcinoma reaching as high as 99.5%. This means that the vast majority of patients can survive long-term even without surgery.

"Many patients diagnosed with thyroid cancer actually have a 'non-fatal cancer'," points out Laura Harper, an oncologist at Memorial Sloan Kettering Cancer Center. She notes that the annual growth rate of papillary microcarcinoma is only 2-3%, and the risk of metastasis is extremely low; excessive surgery can actually increase the risk of complications. Data from South Korea shows that the incidence of postoperative hoarseness and hypoparathyroidism in thyroid cancer patients is 12% and 8%, respectively, with some patients requiring lifelong thyroid hormone replacement therapy. Faced with the dilemma of overdiagnosis, many countries have begun to adjust their treatment strategies. In 2015, the American Thyroid Association issued guidelines recommending "active surveillance" rather than immediate surgery for low-risk papillary microcarcinoma. Since 2020, South Korea has raised the upper age limit for thyroid ultrasound screening from 40 to 50 years old to avoid over-testing. China is following suit; the "Guidelines for the Diagnosis and Treatment of Papillary Thyroid Microcarcinoma" released in 2024 clearly states that for lesions ≤5mm in diameter without high-risk factors, regular follow-up examinations are recommended, without the need for immediate surgery. "The goal of medicine is to prolong life, not to eliminate all cancer cells," emphasized Gao Ming, Chairman of the Thyroid Cancer Professional Committee of the Chinese Anti-Cancer Association. Over-treatment not only increases patients' physical suffering and financial burden but also wastes medical resources. The future direction of diagnosis and treatment should be "precise stratification"—actively treating high-risk patients and appropriately observing low-risk patients.

VI. Response Strategies: A Comprehensive Revolution from Screening to Treatment Faced with the surge in thyroid cancer cases, the world is building a scientific response system encompassing screening, diagnosis, and treatment. At the screening level, experts recommend establishing a "risk-stratified screening" model: the general population should undergo thyroid ultrasound examinations every 2-3 years, while those with high-risk factors such as family history or radiation exposure should be examined annually, avoiding overdiagnosis caused by indiscriminate screening. Advances in diagnostic technology are also contributing to accurate identification. The ThyMet combined with ultrasound prediction model developed by the Chinese Anti-Cancer Association has increased the accuracy rate of differentiating benign from malignant thyroid nodules to 92.3%, effectively reducing unnecessary biopsies. "By using non-invasive blood tests, we can distinguish between benign and malignant nodules, making diagnosis more accurate and safer," explained the research leader. The shift in treatment philosophy is even more crucial. In addition to active monitoring, minimally invasive treatment techniques are gradually being promoted. Ultrasound-guided radiofrequency ablation is as effective as surgery for low-risk thyroid cancers ≤2cm in diameter, but with less trauma, faster recovery, and a postoperative complication rate of only 1.2%. "For patients who wish to preserve thyroid function, minimally invasive treatment is a better option," said Wang Lihua. She added that future treatments will focus more on individualization, developing plans based on factors such as the patient's age, physical condition, and tumor characteristics. From a public health perspective, reducing environmental risks is equally important. Experts are calling for stronger control over endocrine disruptors, limiting harmful chemicals in plastic containers and cosmetics; optimizing iodized salt policies, dynamically adjusting iodine levels based on regional iodine nutrition status; and raising public health awareness to reduce the risk of disease through weight control, regular sleep patterns, and reduced radiation exposure. "The surge in thyroid cancer cases is both a challenge and an opportunity," summarized David Forman, a cancer prevention expert at the World Health Organization. This phenomenon demonstrates the power of medical progress but also exposes shortcomings in the healthcare system. In the future, only by balancing diagnostic accuracy with the boundaries of overtreatment, and by considering both individualized treatment and public health prevention, can we truly address this "silent wave."

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