Interplay of Factors Account for Rise in Thyroid Cancer Diagnoses

Comment: An international panel of thyroid experts composed this clinical review that examines the factors underlying the growing global incidence of thyroid cancer. The authors attributed this rise largely to increased detection of small (<2cm), indolent papillary thyroid cancers that have not been associated with an increase in thyroid cancer mortality. The authors identified increased patient and physician awareness, mass-media influence, economic factors, and disparities in access to healthcare as contributing factors. Specifically, they state: “Patients are generally in favor of public screening strategies and that most consider the identification of small-volume thyroid cancer as potentially lifesaving ,which supports widespread use of diagnostic tests…” —Andres Bur, MD

What factors explain the increasing global incidence of thyroid carcinoma?

Bottom Line: Although there is evidence to suggest that the true disease incidence may be changing slightly, most of the increase in incidence of thyroid cancer is related to factors that promote early diagnosis of low-risk lesions, which is resulting in a significant phenomenon of overdiagnosis.

(click for larger image) Competing factors and their influence on the incidence of thyroid cancer.
© 2017 Wiley Periodicals, Inc.

Background: The incidence of well-differentiated thyroid cancer has been increasing dramatically over the last 20 years worldwide, and is expected to be the fourth most common cancer by 2030. Several studies have shown a generalized rising trend across different continents with dissimilar health systems and ethnicities. Much of the increase is secondary to increased detection of small, low-risk tumors, with questionable clinical significance. The literature suggests a trend to excessive diagnosis due to increasing access to increasingly sensitive tests as the main cause of overdiagnosis. However, there are other factors that may explain this recent change, and identification of these factors would help to direct interventions in order to determine the most rational and cost-effective approach toward identifying patients who have a thyroid carcinoma and are most likely to benefit from interventions.

Study design: Comprehensive literature review. An epidemiological framework that evolved from the classic epidemiological triangle, named “the wheel of causation model,” was adapted.

Synopsis: Articles addressing the causes of the increased incidence were critically reviewed. A complex interplay of environmental, medical, and social pressures has resulted in increased awareness of the thyroid disease risk, increased screening of thyroid cancers, and increased diagnosis of thyroid cancers.

Citation: Sanabria A, Kowalski LP, Shah JP, et al. Growing incidence of thyroid carcinoma in recent years: factors underlying overdiagnosis. Head Neck. 2018;40:855–866.