BACKGROUND
Thyroid nodules are common and up to 65% of the adult population being expected to have this condition. Many thyroid nodules do not result in any symptoms and are not diagnosed. However, the widespread use of radiological tests, such as neck ultrasound, has increased the number of thyroid nodules found on these tests done for other reasons. Biopsy of thyroid nodules can be performed to diagnose cancerous nodules. The decision to undergo this procedure is based on the ultrasound appearance of the thyroid nodules. The use of ultrasound-based riskstratification systems for thyroid nodules has allowed clinicians to avoid numerous unneeded thyroid biopsies.

The cancer risk of thyroid nodules has been estimated to be 5-15%, based on prior studies. This risk could be overestimated if only thyroid nodules referred for biopsy or surgery are evaluated or if thyroid nodules from a center specialized in thyroid cancer treatment are analyzed, since these centers will attract a higher number of cancerous nodules than those existent in the general population. In addition, the cancer risk can be underestimated when thyroid cancer is missed in case of false negative results of the initial biopsy or short follow-up period, since most thyroid nodules have a slow growth rate over years. This study aimed to assess the cancer rate of thyroid nodules larger than 1 cm in diameter diagnosed by ultrasound during long-term follow-up of up to 23 years.

THE FULL ARTICLE TITLE
Grussendorf M et al. Malignancy rates in thyroid nodules: a long-term cohort study of 17,592 patients. Eur Thyroid J. 2022 Jun 29;11(4):e220027. doi: 10.1530/ ETJ-22-0027.

SUMMARY OF THE STUDY
The study included 17,592 consecutive patients diagnosed with a thyroid nodule larger than 1 cm at a single care center in Germany between March 1989 and April 2013. Patients with a nodule larger than 1 cm and one or more ultrasound criteria suspicious for cancer (hypoechoic pattern, irregular margins, microcalcifications) were offered thyroid biopsy. A total of 7776 patients (44.2%) underwent biopsy, while 9816 patients (55.8%) had only a thyroid ultrasound at diagnosis. Based on the results of the initial examination (biopsy with benign results or nonsuspicious features on ultrasound), 9568 patients were discharged from the clinic and not included in the study for further analysis. A total of 1293 patients with thyroid nodules larger than 1 cm were referred for surgery after the initial diagnosis, while 6731 individuals underwent long-term follow-up (up to 23 years, average 5 years).

A total of 189 patients in this study confirmed to have thyroid cancer (1.1% of the entire group). Of these, 155 patients (82%) were diagnosed at the time of the first evaluation. All of the remaining cases confirmed to have thyroid cancer (18% of all cancers) were detected within ten years of follow-up: 25 patients (13.2%) in years 2-5 of follow-up and 9 patients (4.8%) in years 6-10 of follow-up. There were no cancers detected in patients who underwent surgery after 10 years of follow-up. The risk of cancer decreased to 0.14% during the first five years of follow-up, and to 0.05% in years 6-10 of follow-up.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
In this large study with long-term patient follow-up of up to 23 years, the cancer rate of unselected thyroid nodules larger than 1 cm diagnosed on ultrasound was lower than previously reported (1.1% versus 5-15%). During follow-up for more than five years of those patients that did not undergo surgery, the cancer rate dropped to less than 1/1000 cases. These findings may help to reassure patients with newly diagnosed thyroid nodules, and to decrease the number of unneeded diagnostic and therapeutic procedures and shorten the follow-up period.

— Alina Gavrila, MD, MMSC

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