Between 1973 and 2002, the incidence of thyroid cancer in the U.S. increased by more than two-fold. Much of this increase appears to be explained by increased detection of small tumors that may never have become symptomatic. These results were published in the Journal of the American Medical Association.
The thyroid is a gland at the base of the throat. While the incidence of some other cancers has declined over time, the incidence of thyroid cancer has increased greatly in recent years. There are at least two possible explanations for this trend: it’s possible that thyroid cancer is truly occurring more frequently than in the past, but it’s also possible that it’s simply being detected more often. Techniques such as ultrasound and fine-needle biopsy, for example, may allow doctors to identify thyroid cancer that would otherwise have gone undetected.
Detection of a cancer that would never otherwise have caused health problems is referred to as overdiagnosis. As a result of overdiagnosis, some individuals receive cancer diagnoses and treatments that they might otherwise have avoided.
To explore the reasons for the recent increase in thyroid cancer incidence, researchers evaluated a cancer registry that covers roughly 10% of the U.S. population. The researchers explored trends in the types of thyroid cancer diagnoses over time.
- Between 1973 and 2002, the incidence of thyroid cancer increased by more than two-fold (from 3.6 cases of thyroid cancer per 100,000 people per year to 8.7 cases of thyroid cancer per 100,000 people per year).
- Most of the increase was due to an increase in small papillary thyroid cancers (a type of thyroid cancer with a good prognosis).
- The number of deaths from thyroid cancer remained stable during this time period.
Because most of the increase in thyroid cancer incidence was due to an increase in the number of small tumors, and because there was no increase in the death rate, the researchers conclude that the increase in thyroid cancer incidence is more likely due to increased detection of thyroid cancer, rather than to increased occurrence of thyroid cancer. Increased detection of very small thyroid cancers may lead to unnecessary treatment in some patients.
An accompanying editorial cautions that because it’s not possible to tell which tumors will spread and which will not, even patients with small tumors will probably continue to choose to be treated.
Reference: Davies L, Welch HG. Increasing Incidence of Thyroid Cancer in the United States, 1973-2002. JAMA. 2006;295:2164-2167.
Accompanying Editorial: Mazzaferri EL. Managing Small Thyroid Cancers. JAMA. 2006;295:2179-2182.