Papillary thyroid cancer incidence has increased in the United States from 1978 through 2011 for both men and women of all ages and races. Overdiagnosis is partially responsible for this trend, although its magnitude is uncertain. This study examines papillary thyroid cancer incidence according to stage at diagnosis and estimates the proportion of newly diagnosed tumors that are attributable to overdiagnosis. We analyzed stage specific trends in papillary thyroid cancer incidence, 1981-2011, using the Surveillance, Epidemiology and End Results national cancer registries. Yearly changes in early and late-stage thyroid cancer incidence were calculated. We estimate that the proportion of incident papillary thyroid cancers attributable to overdiagnosis in 2011 was 5.5 and 45.5% in men ages 20-49 and 501 and 41.1 and 60.1% in women ages 20-49 and 501, respectively. Overdiagnosis has resulted in an additional 82,000 incident papillary thyroid cancers that likely would never have caused any clinical symptoms. The detection of early-stage papillary thyroid cancer outpaced that of late-stage disease from 1981 through 2011, in part due to overdiagnosis. Further studies into the prevention, risk stratification and optimal treatment of papillary thyroid cancer are warranted in response to these trends.Thyroid cancer incidence rates have increased dramatically over the past three decades in the United States (U.S.) 1 resulting in thyroid cancer now being the fifth most common cancer diagnosed among women.2 This trend contrasts the decreases in incidence observed for other malignancies including lung, colorectal and breast cancer. 3 Additionally, since 1975 the relative five-year survival for papillary thyroid cancer has increased from 92 to 98% with no change in mortality among men and women of all ages and races, 4 indicating that these trends are at least in part due to overdiagnosis or the detection of tumors that are of no clinical relevance. Overdiagnosis has occurred primarily from increased usage of highly sensitive imaging modalities such as computed topography (CT) scan imaging and ultrasonography; technologies that are capable of detecting micro (<1 cm) papillary thyroid cancer. 5-7

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BackgroundSelenium is an essential trace element that is important for thyroid hormone metabolism and has antioxidant properties which protect the thyroid gland from oxidative stress. The association of selenium, as well as intake of other micronutrients, with thyroid cancer is unclear.MethodsWe evaluated associations of dietary selenium, beta-carotene, calcium, vitamin D, vitamin C, vitamin E, folate, magnesium, and zinc intake with thyroid cancer risk in the National Institutes of Health – American Association of Retired Persons Diet and Health Study, a large prospective cohort of 566,398 men and women aged 50–71 years in 1995–1996. Multivariable-adjusted Cox proportional hazards regression was used to examine associations between dietary intake of micronutrients, assessed using a food frequency questionnaire, and thyroid cancer cases, ascertained by linkage to state cancer registries and the National Death Index.ResultsWith the exception of vitamin C, which was associated with an increased risk of thyroid cancer (HRQ5 vs Q1, 1.34; 95% CI, 1.02–1.76; Ptrend, <0.01), we observed no evidence of an association between quintile of selenium (HRQ5 vs Q1, 1.23; 95% CI, 0.92–1.65; Ptrend, 0.26) or other micronutrient intake and thyroid cancer.ConclusionOur study does not suggest strong evidence for an association between dietary intake of selenium or other micronutrients and thyroid cancer risk. More studies are needed to clarify the role of selenium and other micronutrients in thyroid carcinogenesis.