Thyroid cancer in the USA: current trends and outstanding questions

Nearly 15 years has passed since the Davies and Welch publication 1 Davies L Welch HG Increasing incidence of thyroid cancer in the United States, 1973–2002. JAMA. 2006; 295: 2164-2167 Crossref PubMed Scopus (2556) Google Scholar first raised broad awareness about overdiagnosis of thyroid cancer in the USA. Overdiagnosis is the detection of subclinical disease that would have been unlikely to go on to become clinically apparent had it not been found through testing. Between 1973 and 2002, annual incidence of detected thyroid cancer cases increased 240% to 7·7 per 100 000 people. Mortality due to thyroid cancer during that time period was low and had not changed significantly, at 0·5 per 100 000 population. The majority of the incident cases were due to papillary histology, and this was also the type of thyroid cancer that had been responsible for virtually the entire increase in incidence. Davies and Welch 1 Davies L Welch HG Increasing incidence of thyroid cancer in the United States, 1973–2002. JAMA. 2006; 295: 2164-2167 Crossref PubMed Scopus (2556) Google Scholar suggested the detection of subclinical disease was likely the reason for the increase, because papillary thyroid cancer is commonly found at autopsy in people who have died of other causes, never knowing they had a thyroid cancer. A meta-analysis of autopsy studies has since shown that the prevalence of thyroid cancer in people who have died of other causes is 11·2%. 2 Furuya-Kanamori L Bell KJ Clark J Glasziou P Doi SA Prevalence of differentiated thyroid cancer in autopsy studies over six decades: a meta-analysis. J Clin Oncol. 2016; 34: 3672-3679 Crossref PubMed Scopus (105) Google Scholar