Patients who initially received negative thyroid biopsy results might face higher cumulative risk of developing thyroid cancer than that projected in previous literature, according to study results published as a research letter in JAMA Otolaryngology – Head & Neck Surgery.

Researchers conducted a cross-sectional analysis of population-based data to determine patients’ long-term risk of being diagnosed with thyroid cancer after initial benign thyroid biopsy results. The researchers identified all thyroid biopsies linked to the Ontario Cancer Registry that were performed in Ontario, Canada, between January 1991 and December 2010 and followed patients for up to 24 years for diagnoses of differentiated thyroid cancer.

Of the 146,016 adults who underwent ≥1 thyroid biopsy during the study period, 92.9% received initially benign results. The mean age at which negative biopsy was recorded was 52.5, and 81.2% of these individuals were women. In 1991, there were 2280 thyroid biopsies performed with benign results (22.1/100,000 residents). This annual rate rose steadily over time to 12,074 biopsies in 2010 (91.5/100,000 residents), resulting in an approximately 4-fold increase.

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During follow-up with all included participants, the investigators found that 6354 patients who initially had benign results eventually received a diagnosis of thyroid malignant neoplasm (396/100,000 person-years). Patients had a 4.6% cumulative risk for thyroid cancer diagnosis after 10 years and a 7.5% cumulative risk after 24 years, which was higher compared with rates cited in recent literature (0.3% to 2.4% after <10 years of follow-up).

Study limitations included a lack of patient-specific clinical information (eg, ultrasonography, pathology tests). In addition, the definition of benign cytology was variable in Ontario before the adoption of the Bethesda classification, which led to at least 17 years of patient data in this study for which the cytologic findings were not standardized.

“Because cumulative risk of thyroid cancer in these patients is higher than the baseline lifetime risk of the population,” said the researchers, “further large risk stratification studies incorporating standard ultrasound biopsy data are needed to identify those requiring long-term follow-up.”

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Reference

Bongers PJ, Kluijfhout WP, Devon K, et al. Long-term risk of thyroid cancer after initially negative thyroid biopsy results [published online April 18, 2019]. JAMA Otolaryngol Head Neck Surg. doi:10.1001/jamaoto.2019.0386