With thyroid cancer incidence rates rising at a perplexing rate, concerns about overdiagnosis are starting to take center stage. A paper citing a few reasons for this spike in overdiagnosis, and how radiologists can help stem the tide, was recently published online in Academic Radiology.

Authors Jenny K. Hoang, MBBS, of Duke University Medical Center in Durham, N.C., and colleagues cited statistics showing thyroid cancer as the ninth most common cancer in the U.S., fifth most common among women. However, while there were an estimated 62,000 new cases of thyroid cancer in 2014, the number of deaths was estimated at fewer than 1,900. Incidence rates have increased by 185 percent in 35 years, a greater jump than cancers with screening programs like prostate and breast cancers. Spiking rates and a mismatch between incidence and mortality point to a problem with overdiagnosis.

“Given the epidemic of new thyroid cancers due to overdiagnosis, it is critical that radiologists recognize the role of imaging in contributing to the problem,” wrote Hoang and colleagues.

They outlined three main reasons for the growth in thyroid cancer diagnoses:

1. Imaging of incidental thyroid nodules – These nodules are very commonly detected on imaging, though radiologists’ decisions about whether to report and clinicians’ decisions about workup are highly variable, explained Hoang and colleagues. Incidental thyroid nodules are present on 16-25 percent of CT scans, which is lower than other modalities, however the ubiquitous use of CT means that most incidental thyroid nodules receiving workup were first detected on CT. The malignancy rate of incidental nodules on CT and ultrasound is less than 12 percent.
2. They are easy to biopsy – Unlike other incidentalomas found throughout the body, thyroid nodules are superficial and provide an easy target for fine-needle aspiration biopsy. Since it’s a simple and low-risk procedure, Hoang and colleagues suggest that the threshold to biopsy is low and that decisions may not always adhere to recommendations. The number of fine-needle aspiration biopsies for thyroid nodules doubled from 2006 to 2011, which was associated with a 31 percent increase in the number of surgeries for thyroid nodules, according to the authors.
3. Pathology specimens with incidental findings – Routine processing of surgical specimens for goiter and thyrotoxicosis reveal incidental cancers in anywhere from 6-18 percent of patients, according to Hoang and colleagues. Growth in the number of these surgical procedures could be translating to an increase in the incidence of subclinical cancers.

The authors stressed the need to reduce diagnosis of thyroid cancer likely to be indolent by reducing the number of incidental nodules that undergo workup and biopsy. They highlighted the work of the American College of Radiology Incidental Thyroid Findings Committee, of which Hoang is a member. That committee’s recommendations on reporting nodules were based on Duke’s three-tiered categorization system. Patient with suspicious imaging findings should have further workup with dedicated thyroid ultrasound regardless of nodule size. If there are no suspicious imaging findings on CT, MRI or extrathyroidal ultrasound, decisions about further dedicated thyroid ultrasound should be based on patient age and nodule size (younger than 35 years and nodule 1 cm or greater? Send for additional workup. For those 35 or older, 1.5 cm is the cutoff for workup).

 Hoang and colleagues also pointed to the work of Smith-Bindman et al which sought to optimize sonographic criteria for biopsy of thyroid nodules. They found that nodules with microcalcifications, solid composition and a size greater than 2 cm were significantly associated with cancer, and suggested that biopsy be performed on nodules with any two of the these three characteristics.