BACKGROUND
A worldwide increase in the incidence of small papillary thyroid cancers (microcarcinomas) has been observed in the past couple of decades. This trend, however, shows clear regional differences. While the rise in cases of papillary thyroid cancer has increased as much as 10-fold in South Korea, the increase in many northern European countries has been minimal or nonexistent. Further, in the United States, up to 30% of larger nodules that have been diagnosed as papillary thyroid cancers end up being diagnosed as papillary thyroid microcarcinomas at the time of surgery. One factor that explains regional differences in the number of patients with thyroid cancer is the different policies guiding the use of thyroid biopsy. For instance, in the United States, specialists involved in thyroid nodule assessment generally agree to biopsy thyroid nodules >1 cm with suspicious patterns on ultrasound, even if the nodule is not felt on exam. These recommendations contrast with the Dutch national guidelines published in 2007, which recommend biopsies only of palpable thyroid nodules.

These differences in the thresholds for performing thyroid biopsies create an opportunity to examine the role of active surveillance, which is monitoring of suspicious or confirmed low-risk thyroid cancers (usually <1 cm) over time with ultrasound and physical exam and avoiding surgery. Active surveillance has been presented as an approach toward minimizing thyroid cancer overdiagnosis and overtreatment. This study describes characteristics of patients with small papillary thyroid cancers, as well as the proportion of patients who are potential candidates for active surveillance for low-risk thyroid cancers in the Netherlands.

THE FULL ARTICLE TITLE
Lončar I et al 2021 Active surveillance for papillary thyroid microcarcinoma in a population with restrictive diagnostic work-up strategies. Thyroid. Epub 2021 Jan 11. PMID: 33430696.

SUMMARY OF THE STUDY
Data collection was performed using the Netherlands Cancer Registry to identify patients diagnosed and treated for micropapillary thyroid cancer (≤1 cm) in the Netherlands from January 2005 to December 2015. Patients were categorized into three groups according to the indication for surgery: (1) preoperative biopsy–proven spread into the lymph nodes, (2) micropapillary thyroid cancer identified after surgery for another indication (Graves’ disease, multinodular goiter, etc.), and (3) thyroid nodules <1 cm that had been previously biopsied with cytology read as cancer or suspicious for cancer. Cancer recurrence was assessed in all three groups during follow-up.

A total of 6,477 patients were diagnosed with thyroid cancer during this 11-year period. From this group, 1,018 patients fit the criteria to be analyzed. Overall, micropapillary thyroid cancer accounted for 15.7% of the total number of cases of thyroid cancers in that country. The average cancer size was 6 mm. A total of 152 (14.9%) patients were in group 1, 667 (65.5%) patients in group 2 and 199 (19.5%) patients in group 3. As expected for the usual demographics for thyroid cancer, 75.8% of the group was female with an average age of 50 years. Overall, the rate of cancer recurrence was low (3.8%) over an average follow-up time of 68.7 months.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study suggests that papillary thyroid microcarcinomas account for substantially lower proportion of thyroid cancer in the Netherlands than that of many other countries, such as the United States. The authors suggest that this is likely due to the more restrictive use of thyroid biopsies in the Netherlands practiced since 2007, leading, therefore, to less frequent detection of thyroid cancers. Overall, an estimated 3% of all patients with papillary thyroid cancer, and about 20% of patients with micropapillary thyroid cancer, would have been candidates for active surveillance in this population. Further study is needed to determine if the overall survival of patients in the Netherlands is affected by these practices.

— Alan P. Farwell, MD

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