Overdiagnosis Blamed for Global Increase in Thyroid Cancer

Researchers from Italy and France have coauthored an article in the

New England Journal of Medicine

(NEJM) that blames novel diagnostic technologies, increased access to healthcare services, and increased medical surveillance for the thyroid cancer epidemic around the world.

The authors create a case against this data by arguing that the mortality rate for the disease has not changed, while the disease incidence has sky-rocketed—there is food for thought here. A similar argument has been made for over diagnosis of other types of cancers such as breast cancer.

In their current report, the authors reference the dramatic rise in thyroid cancer cases in South Korea—about a 20% increase from 12.2 cases per 100,000 (1993 to 1997) to 59.9 cases per 100,000 (2003 to 2007). While neighboring Japan had good reason to be concerned and more vigilant about incidence of cancer in its population, following the nuclear disaster in Fukushima in 2011, thyroid cancer incidence among screened children and adolescents was about 30-times higher than the national average just a few months earlier. While the rise in incidence among middle-aged (50 to 59 years) Korean women, following the introduction of organized screening programs in 1999, the spike in the United States, Australia, and Italy began in the 1980s around the time when ultrasound was introduced in gynecologic clinics.

Thyroid

A paper published late last year in the journal surveyed the incidence rate of thyroid cancer in other affluent countries across the globe and concluded that improved diagnostic technologies were responsible for nearly 60% of thyroid cancer cases diagnosed between 2003 and 2007, in women younger than 80 years of age, in France, Italy, United States, Australia, and the Republic of Korea. High resource countries, the authors concluded, will continue to see this trend and they stressed the need for better regulation.

Based on their analysis of populations in 12 countries, the authors in the NEJM paper conclude that over diagnosis during the period between 2003 and 2007 could have led to the diagnosis of 90% of thyroid-cancer cases among women in South Korea; 70% to 80% of cases in United States, France, Italy, and Australia; and 50% in Japan, Nordic nations, England, and Scotland. While the raw number of over diagnosed cases were much lower among men, they did exist. During the same time period, the authors estimate that 70% of thyroid cancer cases among men in France, Italy, and South Korea were a result of over diagnosis; the number hovered around 45% in the United States and Australia.

Overall, 470,000 women and 90,000 men across 12 countries were potentially over diagnosed as having thyroid cancer, the analysis estimates. Since the authors found little evidence of new risk factors or exposure to potential carcinogens, they conclude that “access to health care, physicians’ practices, and the extent of intentional inspection of the thyroid gland or incidental findings are the most likely explanations of our findings.”

The crux of the problem is deciding between watchful waiting and treatment—the authors write that small papillary lesions in the thyroid gland can be left untouched and are potentially nonlethal. Therefore, unnecessary resection of the thyroid gland and potentially debilitating treatments such as radiation are a serious adverse effect of over diagnosis among these individuals, and should be prevented.

Reference

N Engl J Med

Vaccarella S, Franceschi S, Bray F, Wild CP, Plummer M, Dal Maso L. Worldwide thyroid-cancer epidemic? The increasing impact of overdiagnosis. . 2016;375(7):614-617. doi: 10.1056/NEJMp1604412.