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Re: Brito et al., overdiagnosis of thyroid cancer and Graves' disease.

In the letter to the editor written by Brito et al. (1), the authors weigh in on the debate as to whether thyroid cancer incidence trends reflect a true increase in thyroid tumors or an artifact of improved detection modalities and a subsequent detection bias. They cite two recently published articles in Thyroid (2,3) as evidence that thyroid cancer is being overdiagnosed and overtreated. We agree that improvements in technology, as well as increased access to better imaging, has likely been partly responsible for an increase in thyroid cancer detection. However, we would also argue that there is a substantial amount of evidence in the literature supporting the idea that something more than just improved diagnosis is impacting thyroid cancer trends. Brito et al. address the increasing papillary thyroid cancer incidence trends in their introduction by stating, ‘‘neither new effective treatments nor the emergence of a subtype of nonlethal thyroid cancer can explain this phenomenon’’ (1). However, it is unclear why the emergence of a new subtype would be necessary to cause an increase in papillary thyroid cancer incidence. It is also possible that an unexpected or unidentified increase in exposure to an environmental risk factor such as radiation from medical imaging, endocrine disruptors in the environment, or even an unidentified environmental exposure could also lead to such an increase (4). Currently, there are no data directly linking increased environmental exposures to increased thyroid cancer rates. However, when one critically reviews the literature, there are also no studies that directly link the increased use of imaging and FNA to the higher thyroid cancer rates. All the studies on this subject have inferred such a link. However, no large-scale investigation of the direct cause–effect of FNA–thyroid cancer has been accomplished or a reliable estimate of the proportion of new thyroid cancers attributable to FNA reported. In a recently published article in Thyroid (5), we reported on the papillary:follicular thyroid cancer incidence rate ratios. In this study, we illustrated a significant increase in the proportion of papillary thyroid tumors over time compared to follicular cancers. In fact, the rate of follicular cancers has barely increased over time. Because imaging studies cannot discriminate pathologic type, why would they not also increase the rate of follicular thyroid cancer detection as well? One argument is that there is not as large a ‘‘pool’’ of follicular cancers to be diagnosed. However, it is unlikely that, prior to these imaging modalities being available, 100% of follicular thyroid cancers were diagnosed in the past. Thus, a pool of undiagnosed follicular cancers likely also exists, yet they are not being discovered by the increased use of imaging. In fact, we would argue that the lack of an increase in follicular thyroid cancer rates along with the significant change in the relative distribution of the known thyroid tumor types over time is a very important part of the conversation that argues against overdiagnosis in this case. The authors also suggest that better access to healthcare leads to higher rates of papillary thyroid cancer diagnosis by pointing out, ‘‘Morris et al. showed that the incidence of thyroid cancer increased faster in patients who had healthcare insurance through Medicare and thus, had more access to healthcare’’ (1). We would argue that age itself is a confounder in an analysis such as this because thyroid cancer is known to grow very slowly, and even though thyroid cancer does occur in young people, on average it is a cancer that is diagnosed later in life. It should also be noted that when evaluating the age-specific trends, a peak in thyroid incidence is not observed at the age of 65 (6). In the National Cancer Institute’s