Doctors weigh whether medical imaging is driving rise in thyroid cancer among young people

Just 31 and feeling well, special needs teacher Jess Cain was stunned when a lump felt during a massage led to a diagnosis of thyroid cancer and rapid surgery. Her case is one of many that doctors and researchers say illustrate a broader rise in thyroid cancer diagnoses, particularly among younger adults and women.

Thyroid cancer, which affects the small butterfly-shaped gland in the neck that controls metabolism and other functions, has increased substantially in many countries over the past two decades. In the U.K., diagnoses rose by 62 percent in 10 years and are projected to climb by nearly three-quarters by 2035. Overall cases have almost tripled in three decades, and women are diagnosed at nearly four times the rate of men.

Clinicians and public health researchers are debating why the numbers are climbing. Some experts say improvements in imaging and more frequent medical testing mean clinicians are detecting small, slow-growing tumours that might otherwise never have caused symptoms. Others contend the rise cannot be explained by detection alone and point to increased exposure to ionizing radiation from medical scans as a likely contributor.

"There’s no doubt of an increase in the incidence of thyroid cancer over the past 25 years," said Professor Fausto Palazzo, an endocrine surgeon at Hammersmith Hospital in London. "In large part, we believe it’s related to the fact that we’re simply detecting more disease. But that doesn’t mean more cancers aren’t developing than before. It just makes it more difficult to interpret."

Supporters of the overdetection explanation note that more sensitive ultrasound, CT and other imaging make it easier to find small thyroid nodules. Opponents say registry and mortality data suggest a genuine increase in clinically significant disease. In a 2020 analysis of 18 years of California registry data, Dr. Riccardo Vigneri, emeritus professor of endocrinology at the University of Catania, reported rises in larger, more advanced tumours and in deaths, which he argued could not be accounted for solely by overdetection.

Historically, acute radiation exposure from nuclear events such as atomic bombings and the Chernobyl disaster was linked to sharp rises in thyroid tumours among children. Today, the largest source of man-made ionizing radiation for many people is medical imaging. A landmark analysis of radiation exposure in the U.S. from 1980 to 2006 found the average dose received by Americans doubled in that period, with CT scans responsible for more than half of the increase and about one-third of CTs aimed at the head and neck.

Epidemiological studies have tied childhood CT scans to later thyroid cancer risk. A study of more than 11 million Australians found children who underwent CT scans had a 40 percent higher risk of thyroid cancer later in life. A separate analysis published this year estimated that about 5 percent of new cancers in the United States could be linked to CT scans, a burden comparable to that attributed to alcohol in some studies. Experts caution, however, that CT scans are often clinically necessary and can be lifesaving, and that individual risk from a single scan remains small.

"The only two things we know that increase the chance of thyroid cancer are genetic history and radiation exposure," Palazzo said. He added that while environmental increases in radiation exposure remain difficult to prove, they are plausible contributors to the rising incidence.

Researchers are also exploring a range of other potential environmental and lifestyle factors. Iodine deficiency, which can cause the thyroid to enlarge, has been proposed as one contributor. A 2010 study of more than 700 U.K. schoolgirls found over two-thirds had low iodine levels; historically, milk had been a major source of dietary iodine in Britain but consumption patterns and dairy-free diets have changed.

Other studies have investigated links to endocrine-disrupting chemicals, airborne pollution and radon gas. A 2022 analysis from researchers in Beijing reported higher thyroid cancer rates in areas with poor air quality, and studies from the U.S. and Egypt have suggested certain man-made chemicals can impair thyroid function. A team at the University of Guam reported possible associations between residential radon exposure and thyroid cancer, though many experts say evidence remains preliminary and that large-scale epidemiological research is needed to clarify contributions.

The substantially higher incidence in women has generated additional inquiry. Clinicians suggest hormonal differences may play a role: rates of thyroid cancer converge between men and women after menopause, which points to possible influences from sex hormones. Autoimmune thyroid conditions, which are more common in women and cause chronic inflammation, may also increase cellular susceptibility to mutation, said Dr. Jahangir Ahmed, a consultant ear, nose and throat surgeon.

Despite rising incidence, prognosis for most thyroid cancers is favorable. The two most common forms, papillary and follicular thyroid cancer, are typically slow-growing and highly treatable. "If you catch it in a reasonable time, more than 90 percent of patients can be cured," Ahmed said. Standard treatment often involves surgical removal of part or all of the thyroid, and some patients receive radioactive iodine therapy to eliminate residual disease. For very small tumours under 1 centimeter, clinicians increasingly consider active surveillance rather than immediate surgery.

Symptoms that should prompt assessment include a lump in the throat or neck, a hoarse voice lasting more than three weeks, breathing difficulty or trouble swallowing. Public-health messaging has emphasized that while most thyroid cancers have good outcomes, patients with persistent symptoms should seek medical attention.

Clinicians and policy makers face a complex challenge balancing the benefits of diagnostic imaging against potential long-term risks. Professional groups have urged judicious use of CT scans, especially in children, and continued efforts to minimize radiation dose when imaging is necessary. At the same time, researchers say more high-quality, population-level studies are needed to disentangle the relative roles of detection, medical radiation, diet, environmental pollutants and other factors in the rising incidence.

For patients such as Cain, the human toll is immediate. She has undergone thyroidectomy, radioactive iodine therapy and further surgery for recurrent disease. "People refer to it as ‘the good cancer’ because it’s easily treated, but it’s already been two years with it for me and I’ve already had a resurgence within three months of getting the all-clear," she said. Her experience underscores both the potential personal consequences of the disease and the complexity of interpreting trends that combine increased diagnosis with possible changes in underlying risk.

Researchers and clinicians say clearer answers will require coordinated epidemiological studies that track imaging exposure, environmental measures and clinical outcomes over time, together with continued efforts to limit unnecessary radiation exposure and to target screening and treatment decisions according to the best available evidence.