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.
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