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Annual thyroid cancer incidence may be stabilizing
The annual incidence of thyroid cancer, which rapidly increased over the last 3 decades, appears to have leveled off after 2009, according to results of a SEER analysis.
“The rapidly rising incidence of thyroid cancer in the United States has been recognized as an ‘epidemic of diagnosis’ more than an epidemic of disease. Acknowledging this, practice guidelines are becoming increasingly nuanced in recommendations about which nodules to biopsy,” Luc G.T. Morris, MD, Catherine and Frederick R. Adler chair for junior faculty and surgeon at Memorial Sloan Kettering Cancer Center, and colleagues wrote.
Luc G.T. Morris
“The rising diagnosis of thyroid cancer has been linked to increasing health care utilization and imaging practices, which have led to the increased discovery of small papillary thyroid cancers, which generally exhibit indolent behavior,” they added.
Thyroid cancer incidence has tripled in the past 30 years, which can primarily be attributable to the widespread diagnosis of subclinical disease.
Morris and colleagues evaluated 1983 to 2012 SEER data to identify recent trends in thyroid cancer incidence adjusted for age and delayed reporting.
Researchers found an annual percentage change (APC) increase of nearly 3% (APC = 2.99, 95%, 2.3-3.68) from 1988 to 1998. The APC increased substantially in the following decade, from 1998 to 2009 (APC = 6.71, 95% CI, 6.1 to 7.32).
However, the APC leveled off from 2010 to 2012 (APC = 1.75, 95% CI, –1.9 to 5.54).
Incidence rates remained unchanged when researchers adjusted for delayed reporting (2009-2012; APC = 1.54; 95% CI, –2.08 to 5.3).
The stabilization in incidence rates in the most recently evaluated years persisted in analyses stratified by tumor size (tumors 1 cm, APC = 1.25; 95% CI, –7.22 to 10.5). Previously, the incidence of subclinical tumors had increased by more than 9% each year (1996-2009, APC = 9.41; 95% CI, 8.29-10.55)
Positive inflection points — which indicate an accelerated incidence of thyroid cancer — occurred in the 1990s, but negative inflections, which show a decelerating rate, occurred after 2009.
Researchers noted that no known biological risk factors for thyroid cancer followed these incidence rates trends.
Rather, these data might show a shift in medical practices. The American Thyroid Association 2009 guidelines suggested tumor size and ultrasonographic appearance should play a role in choosing whether to biopsy the tumor and discouraged against the biopsy of smaller tumors.
“The data reported here suggest that clinical practices are also changing, as reflected by the beginning of stabilization of the previously rapidly rising incidence of thyroid cancer in the United States,” Morris and colleagues wrote.
“These data cannot provide causal evidence of a link between trends in the incidence of thyroid cancer and specific clinical practice guidelines,” they added. “Nevertheless, the data suggest that changing clinical practices are responsible for the slowing increase in the reported incidence of thyroid cancer.”
More research is required to evaluate whether the incidence of thyroid cancer has reached a plateau near the prevalence of subclinical thyroid cancers in the U.S. population. – by Nick Andrews
Disclosure : The researchers report no relevant financial disclosures.