Over the past couple of decades, there has been a significant increase in the incidence of thyroid cancer throughout the world. This phenomenon is mainly seen in “high income” countries of North America, Europe, and Asia. In the United States alone, the annual incidence has tripled between 1975 and 2009. The upsurge involves papillary thyroid carcinoma (PTC), which comprises 90% of all thyroid cancers. It is also the least aggressive, as evidenced by no increase in death rate from its surge.
Why is this happening? A study published in the New England Journal of Medicine ( NEJM, August 2016) sought to find out the reason for the thyroid cancer “epidemic.” The researchers looked at cancer registry data from multiple countries and compared the change over time. The countries with the highest prevalence of thyroid cancer had two common denominators: improved access to diagnostic tests (ultrasounds, CT scans, and MRIs) and routine cancer surveillance. Since there has not been any emergence of new risk factors for thyroid cancer, “more testing” seems to be the cause for the increase.
The researchers concluded that the rise in PTC was attributed to overdiagnosis rather than increase in occurrence of thyroid cancer. Since ultrasounds became available in the 1970s, small thyroid growths are being increasingly discovered through imaging, often unintentionally. According to the researchers, 70-80% of thyroid cancers in the United States result from overdiagnosis of small, benign tumors. Between 1988-2007, there have been an estimated 228,000 such cases in the United States.
Why should we be concerned? The problem with overdiagnosis is overtreatment. The incidental discovery of small thyroid growths, that would have otherwise remained silent, creates a management challenge for physicians. The name “PTC” further increases anxiety for patients, likely resulting in surgical removal. The researchers reported that a large number of the people in the study had surgical treatment, suggesting that many people are getting aggressive management for benign lesions that could have been managed conservatively.
Thyroidectomy (total or partial removal of the thyroid gland) has to be done by an experienced surgeon; and even then, it comes with a risk of injury to adjacent organs like parathyroid glands and vocal cords (voice box). Such treatment may also involve lymph node removal and radiation therapy, offering additional risks. A study in Japan showed that, in small papillary thyroid cancers, the outcome was the same whether managed by surgery or careful surveillance. In 1,235 patients, only 3.5% of the tumors progressed; and after follow up for 75 months, there were no deaths from these thyroid tumors. Another problem with the PTC epidemic is the rising cost of care; in the United States alone, it was estimated to be $1.6 billion in 2013.
What is the solution? The medical community is taking steps to mitigate the issue. In 2015, the American Thyroid Society (ATS) revised its guidelines on the management of small thyroid nodules (<1cm in diameter) in favor of a “watch and wait” approach. In April 2016, a group of expert pathologists and clinicians renamed a variant of PTC which is shown to have a benign course. In a report published by the Journal of American Medical Association (JAMA), the tumor was reclassified as a "noninvasive neoplasm". The removal of the word “cancer” emphasized the tumor’s low malignancy potential.
These changes offer new guidance for physicians in making evidence-based decisions for management of small, incidental thyroid tumors, while also offering patients conservative treatment options.