Researchers are recommending a more selective approach to biopsy of thyroid nodules after finding that only three nodule characteristics found on thyroid ultrasound imaging were associated with the risk for thyroid cancer: microcalcifications, size greater than 2 cm, and an entirely solid composition.

“Compared with other existing guidelines, many of which are complicated to apply, following these simple, evidence-based guidelines would substantially decrease the number of thyroid biopsies in the United States, asserted study lead author Rebecca Smith-Bindman, MD, in a statement from the University of California–San Francisco (UCSF), where Bindman is a professor in the Department of Radiology and Biomedical Imaging and in the Department of Epidemiology and Biostatistics. “Right now, we’re doing far too many thyroid biopsies in patients who are really at very low risk of having thyroid cancer.”

According to information in the UCSF statement, National Cancer Institute data indicate that an estimated 14,910 men and 45,310 women will have received a diagnosis of thyroid cancer in 2013 and that 1,850 of these patients will die as a result of the disease.

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As Bindman and colleagues noted in JAMA Internal Medicine, the management of thyroid nodules identified on ultrasound imaging varies widely, and although thyroid nodules are common, most (98.4%) are benign.

“[This highlights] the importance of being prudent in deciding which nodules should be sampled to reduce unnecessary biopsies,” wrote Bindman’s group. “Adoption of uniform standards for the interpretation of thyroid sonograms would be a first step toward standardizing the diagnosis and treatment of thyroid cancer and limiting unnecessary diagnostic testing and treatment.”

The investigators’ retrospective case-control study of patients who underwent thyroid ultrasound imaging from January 2000 through March 2005 showed that a total of 8,806 persons were given 11,618 thyroid ultrasound examinations during the study period. Of those patients, 105 subsequently received a diagnosis of thyroid cancer.

Thyroid nodules were common among persons who were given a thyroid cancer diagnosis (96.9%), and also in patients who were not (56.4%). The only nodule-related ultrasound findings associated with the risk for thyroid cancer were microcalcifications larger than 2 cm and solid rather than cyst-like in composition.

Bindman’s team determined that if one of those characteristics was to be used as an indication for biopsy, most cases of thyroid cancer would be detected (sensitivity 88%), with a high false-positive rate (44%) and a low positive likelihood ratio (2.0), and 56 biopsies would be performed for each cancer diagnosis. If two of the characteristics were required for biopsy, the sensitivity rate would be lower (52%) but so would the false-positive rate (7%), the positive likelihood ratio would be higher (7.1), and only     16 biopsies would be performed per cancer diagnosis.

“Compared with performing biopsy of all thyroid nodules larger than 5 mm     [0.5 cm], adoption of this more stringent rule requiring two abnormal nodule characteristics to prompt biopsy would reduce unnecessary biopsies by 90% while maintaining a low risk of cancer (5 per 1,000 patients for whom biopsy is deferred),” concluded the authors, who added that their results should be validated in a larger, prospective cohort.