Since the early 1980s, a steady increase in the prevalence of thyroid cancer has been attributed to an increase in screening in recent years and the diagnosis of more small tumors. But according to investigators at the American Cancer Society in Atlanta, factors such as environmental exposures, dietary changes, or genetic causes may play a larger role.
The study aim was to determine whether the increasing incidence of thyroid cancer is confined solely to the diagnosis of smaller tumors. For this, Dr. Amy Y. Chen and her colleagues used the National Cancer Institute’s SEER cancer registry to identify cases of differentiated thyroid cancer diagnosed between 1988 and 2005.
The study cohort involved more than 30,000 cases. The sizes of the tumor were less than 1 cm (25%), 1-2.9 cm (42%), 3-3.9 cm (9%), and 4 cm or larger (11%); 12% had unknown measurements.
The authors reported that, although the age-adjusted incidence of thyroid cancer was thrice among women than among men, patterns of increasing incidence were similar for both sexes.
Specifically, among women, the age-adjusted incidence in cases per 100,000 increased from 6.4 to 14.9 from 1998 to 2005. The annual percentage change of 3.7 per 100,000 was relatively stable during the first decade, but then it more than doubled between 1998 and 2005.
Among men, the age-adjusted incidence in cases per 100,000 increased from 2.5 to 5.1 from 1988 to 2005. Men exhibited annual percentage change of 2.9 per 100,000 cases during the first phase, and 6.3 per 100,000 after 1999.
Our principal finding, Dr. Chen and associates write, was that the greatest increase was for occult tumors; however, an increase in thyroid cancer of all sizes also was observed, including those > 4 cm and those with distant disease.
Despite the better detection of cancers at earlier stages, they note, survival rates did not improve among men or women, suggesting the need for further exploration into the etiologies of increasing thyroid rates.