Increasing incidence of thyroid cancer in the commonwealth of Pennsylvania

IMPORTANCE: The incidence of thyroid cancer in the United States has increased rapidly and Pennsylvania is the state with the highest rate of thyroid cancer in the country, although the factors driving this increase are unknown. Moreover, it remains unclear whether the increase in thyroid cancer represents a true increase in disease or is the result of overdiagnosis. OBJECTIVE: To compare the increase in thyroid cancer incidence and tumor characteristics in Pennsylvania with the rest of the United States and gain insight into the factors influencing the increased incidence of thyroid cancer. DESIGN, SETTING, AND PARTICIPANTS: In a population-based study, data on thyroid cancer from the Surveillance Epidemiology and End Results 9 (SEER-9) registry and the Pennsylvania Cancer Registry (PCR) from 1985 through 2009 were collected and reviewed for information regarding sex, race, histologic type of thyroid cancer, staging, and tumor size at diagnosis. International Classification of Diseases for Oncology, Third Edition code C739 (thyroid carcinoma) was used to identify 110 615 records in the SEER-9 registry and 29 030 records in the PCR. MAIN OUTCOMES AND MEASURES: Average annual percent change (AAPC) in thyroid cancer incidence across various demographic groups in Pennsylvania. RESULTS: The AAPC for thyroid cancer in Pennsylvania was 7.1%per year (95%CI, 6.3%-7.9%) vs 4.2%(95%CI, 3.7%-4.7%) per year in the remainder of the United States, and trends in incidence were significantly different (P < .001). Females experienced a higher AAPC (7.6% per year; 95%CI, 6.9%-8.3%) compared with males (6.1% per year; 95%CI, 4.9%-7.2%) (P < .01), and trend analysis revealed that thyroid cancer may be increasing more rapidly among black females (8.6%per year; 95%CI, 5.4%-11.9%) than among white females (7.6% per year; 95%CI, 6.8%-8.4) (P = .60; but despite the similarity in AAPC between the 2 groups, the joinpoint models fit to the data were not parallel [P < .005]). The rate of tumors with regional (7.0%per year; 95%CI, 5.8%-8.1%) or distant (1.1%per year; 95%CI, 0.3%-1.8%) spread (P < .05) and tumors that were 2 to 4 cm(7.1% per year; 95%CI, 5.2%-9.0%) (P < .05) or larger than 4 cm(6.4%per year; 95%CI, 4.5%-8.2%) (P < .05) at diagnosis also increased. CONCLUSIONS AND RELEVANCE: The incidence of thyroid cancer is rising at a faster rate in Pennsylvania than in the rest of the nation, as is the rate of tumors that are larger and higher stage at diagnosis. These findings suggest that rising disease burden has contributed to the increased incidence of thyroid cancer. Etiologic factors promoting the rise in thyroid cancer in Pennsylvania must be investigated and may provide insight into the drivers of the national increase in thyroid cancer.