Incidence of thyroid cancer has been increasing worldwide with a 3-fold increase in the US since the 1990s. The degree to which this increase is due to a true increase in incidence or reflects the ways that thyroid cancer is found with modern technology (the mode of detection) is a question that has not been broadly examined. Thyroid cancer, like prostate cancer, is a disease that people can die with, never knowing they had it. To this end, determining how mode of detection plays a role in increased incidence is critical to understanding trends in epidemiologic data.
University of Vermont (UVM) Cancer Center member and UVM Larner College of Medicine Assistant Professor, Mirabelle Sajisevi, MD and senior author Louise Davies, MD, UVM alum BS - 1992 and residency 2003, now of Geisel School of Medicine at Dartmouth, and colleagues conducted a retrospective analysis of over one-thousand patients in four countries (South Africa, Denmark, the United States of America, and Canada) who had undergone thyroid-directed surgery to determine how thyroid nodules and cancers come to attention. In addition, the authors set out to see if modes of detection varied depending on geographic region.
As published in JAMA Otolaryngology - Head and Neck Surgery, their findings show geographical variation in modes of detection. The researchers found that in South Africa and Denmark, cancers and nodules were found more often because patients had symptoms, while in the USA and Canada, cancers and nodules were found more often in the course of health care for other issues – patients had no symptoms referable to the thyroid finding. Among patients whose thyroid finding was found in the absence of symptoms, the study found that most frequent mode of detection was what the researchers termed ‘radiologic serendipity’, a thyroid nodule is discovered in an asymptomatic individual undergoing the test for a different reason. Pathologic analysis (across all four countries) revealed that cancers in about half of the cases were in asymptomatic individuals. The authors conclude that the detection of thyroid cancer in asymptomatic individuals has led, at least in part, if not completely, to the rise in thyroid cancer incidence.
Given the large number of asymptomatic patients with thyroid nodules, the authors are now evaluating the use of educational outreach and monitoring approaches for patients with low-risk thyroid nodules and cancers, to decrease the risk of overtreatment in the future.