Review Study Suggests an Overdiagnosis and Overtreatment in Thyroid Cancer
The researchers had previously reported a doubling of thyroid cancer incidence—largely due to the detection of small papillary cancers. Because these tumors are commonly found in people who have died of other causes, and because thyroid cancer mortality had been stable according to data from the Surveillance, Epidemiology, and End Results (SEER) program, Davies and Welch argue that the increased incidence represented overdiagnosis. Thyroid cancer mortality rates were collected from the National Vital Statistics System.
The authors report that since 1975, the incidence of thyroid cancer has now nearly tripled, going from 4.9 to 14.3 per 100 000 individuals (absolute increase, 9.4 per 100 000; relative rate [RR], 2.9; 95% CI, 2.7-3.1). That increase was due to papillary thyroid cancer.
The absolute increase in thyroid cancer in women (from 6.5 to 21.4 = 14.9 per 100 000 women) was almost 4 times greater than that of men (from 3.1 to 6.9 = 3.8 per 100 000 men). The mortality rate from thyroid cancer was stable between 1975 and 2009 (approximately 0.5 deaths per 100 000).
The researchers conclude that the increased incidence is not due to an “epidemic of disease, but rather an epidemic of diagnosis.” They note that the problem is particularly acute for women, who have lower autopsy prevalence of thyroid cancer than men but higher cancer detection rates by a 3:1 ratio.
In a commentary that appeared in Clinical Oncology News, John H. Kim, MD, an associate professor of surgery at the City of Hope in California, says “overdiagnosis” is the wrong term to use. His argument is that data from the SEER database and the National Center for Vital Statistics have limitations. He writes that “one assumption pointing to overdiagnosis is made simply because there is a large increase in incidence of thyroid cancer while mortality remains stable. The implication made is that most of the new cancers identified are not killing patients. Notwithstanding the inability to identify which new cancers identified are killing the patients and which ones aren’t, this assumption simply has not been tested at all in this study.”