Among patients in the United States diagnosed with thyroid cancer from 1974-2013, the overall incidence of thyroid cancer increased 3% annually, with increases in the incidence rate and thyroid cancer mortality rate for advanced-stage papillary thyroid cancer. These findings are consistent with a true increase in the occurrence of thyroid cancer in the United States.

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During the past few decades, the incidence of thyroid cancer has increased substantially in many countries, including the USA. The rise in incidence seems to be attributable both to the growing use of diagnostic imaging and fine-needle aspiration biopsy, which has led to enhanced detection and diagnosis of subclinical thyroid cancers, and environmental factors. The latest American Thyroid Association (ATA) practice guidelines for the management of adult patients with thyroid nodules and differentiated thyroid cancer differ substantially from the previous ATA guidelines published in 2009. Specifically, the problems of overdiagnosis and overtreatment of a disease that is typically indolent, where treatment-related morbidity might not be justified by a survival benefit, now seem to be acknowledged. As few modifiable risk factors for thyroid cancer have been established, the specific environmental factors that have contributed to the rising incidence of thyroid cancer remain speculative. However, the findings of several large, well-designed epidemiological studies have provided new information about exposures (such as obesity) that might influence the development of thyroid cancer. In this Review, we describe the changing incidence of thyroid cancer, suggest potential explanations for these trends, emphasize the implications for patients and highlight ongoing and potential strategies to combat this growing clinical and public health issue.

ResultsOver follow-up, 53,944 men and 24,475 women were diagnosed with a primary cancer. Compared with levels less than 160 mg/dL, high total cholesterol (Ն 240 mg/dL) was positively associated with prostate cancer (hazard ratio [HR], 1.24; 95% CI, 1.07 to 1.44; P trend ϭ .001) and colon cancer (HR, 1.12; 95% CI, 1.00 to 1.25; P trend ϭ .05) in men and breast cancer in women (HR, 1.17; 95% CI, 1.03 to 1.33; P trend ϭ .03). Higher total cholesterol was associated with a lower incidence of liver cancer (men: HR, 0.42; 95% CI, 0.38 to 0.45; P trend Ͻ .001; women: HR, 0.32; 95% CI, 0.27 to 0.39; P trend Ͻ .001), stomach cancer (men: HR, 0.87; 95% CI, 0.82 to 0.93; P trend Յ .001; women: HR, 0.86; 95% CI, 0.77 to 0.97; P trend ϭ .06), and, in men, lung cancer (HR, 0.89; 95% CI, 0.82 to 0.96; P trend Ͻ .001). Results for liver cancer were slightly attenuated after additional adjustment for liver enzyme levels and hepatitis B surface antigen status (men: HR, 0.60; P trend Ͻ .001; women: HR, 0.46; P trend ϭ .003) and exclusion of the first 10 years of follow-up (men: HR, 0.59; P trend Ͻ .001; women: HR, 0.44; P trend Ͻ .001). Total cholesterol was inversely associated with all-cancer incidence in both men (HR, 0.84; 95% CI, 0.81 to 0.86; P trend Ͻ .001) and women (HR, 0.91; 95% CI, 0.87 to 0.95; P trend Ͻ .001), but these associations were attenuated after excluding incident liver cancers (men: HR, 0.95; P trend Ͻ .001; women: HR, 0.98; P trend ϭ .32). ConclusionIn this large prospective study, we found that total cholesterol was associated with the risk of several different cancers, although these relationships differed markedly by cancer site. Oncol 29:1592Oncol 29: -1598 J Clin