Thyroid Research Thyroid Research Archive Thyroid Cancer

The increasing incidence of thyroid cancer is due to detection of very small papillary carcinomas

(July 2006)

The background of the study. In recent years the frequency of thyroid cancer has increased in the United States and other countries. This study was done to determine if the increase was due to a true increase in thyroid cancer or detection of small, previously unrecognized cancers.

How the study was done. Data on the annual incidence of thyroid cancer and the size of the cancers were obtained from the Surveillance, Epidemiology, and End Results (SEER) program of the National Cancer Institute. This program collects annual data on cancer incidence from cancer registries of five states and four metropolitan areas; these areas constitute approximately 10 percent of the U.S. population. Frequency data were available for 1973 to 2002 and tumor-size data for 1988 to 2002. Data on thyroid-cancer mortality for 1973 to 2002 were obtained from the National Vital Statistics System. The overall annual incidence and mortality from thyroid cancer were calculated based on these data.

The results of the study. In 2002, approximately 2400 people (73 percent women) were found to have thyroid cancer in the nine SEER regions. Most (88 percent) of the cancers were papillary carcinomas, 9 percent were follicular carcinomas, and 3 percent were medullary or anaplastic carcinomas.

In 1973, the incidence of thyroid cancer was 3.6 per 100,000 people, and it was 8.7 per 100,000 in 2002. The incidence of papillary carcinoma increased in parallel, from 2.7 per 100,000 in 1973 to 7.7 per 100,000 in 2002. There was no change in the incidence of the other types of thyroid cancer during the same period.

The increase in incidence of papillary carcinoma was due mostly to an increase in small tumors. Tumors ≤1.0 cm accounted for 49 percent and tumors ≤2.0 cm for 87 percent of the increase in incidence of papillary carcinoma from 1988 to 2002.

The mortality rate from thyroid cancer did not change from 1973 to 2002.

The conclusions of the study. The incidence of thyroid cancer has increased from 1973 to 2002 in the United States, due to an increase in detection of very small papillary carcinomas. There was no increase in mortality from thyroid cancer during the same interval.

The original article. Davies L, Welch HG. Increasing incidence of thyroid cancer in the United States, 1973-2002. JAMA 2006;295:2164-7.