Importance: We have previously reported on a doubling of thyroid cancer incidence-largely due to the detection of small papillary cancers. Because they are commonly found in people who have died of other causes, and because thyroid cancer mortality had been stable, we argued that the increased incidence represented overdiagnosis.
Objective: To determine whether thyroid cancer incidence has stabilized.
Design: Analysis of secular trends in patients diagnosed with thyroid cancer, 1975 to 2009, using the Surveillance, Epidemiology, and End Results (SEER) program and thyroid cancer mortality from the National Vital Statistics System.
Setting: Nine SEER areas (SEER 9): Atlanta, Georgia; Connecticut; Detroit, Michigan; Hawaii; Iowa; New Mexico; San Francisco-Oakland, California; Seattle-Puget Sound, Washington; and Utah.
Participants: Men and women older than 18 years diagnosed as having a thyroid cancer between 1975 and 2009 who lived in the SEER 9 areas.
Main outcomes and measures: Thyroid cancer incidence, histologic type, tumor size, and patient mortality. RESULTS Since 1975, the incidence of thyroid cancer has now nearly tripled, from 4.9 to 14.3 per 100,000 individuals (absolute increase, 9.4 per 100,000; relative rate [RR], 2.9; 95% CI, 2.7-3.1). Virtually the entire increase was attributable to papillary thyroid cancer: from 3.4 to 12.5 per 100,000 (absolute increase, 9.1 per 100,000; RR, 3.7; 95% CI, 3.4-4.0). The absolute increase in thyroid cancer in women (from 6.5 to 21.4 = 14.9 per 100,000 women) was almost 4 times greater than that of men (from 3.1 to 6.9 = 3.8 per 100,000 men). The mortality rate from thyroid cancer was stable between 1975 and 2009 (approximately 0.5 deaths per 100,000).
Conclusions and relevance: There is an ongoing epidemic of thyroid cancer in the United States. The epidemiology of the increased incidence, however, suggests that it is not an epidemic of disease but rather an epidemic of diagnosis. The problem is particularly acute for women, who have lower autopsy prevalence of thyroid cancer than men but higher cancer detection rates by a 3:1 ratio.