BACKGROUND
Thyroid nodules are the most common endocrine problem, occurring in up to half of the general populations. Many of these nodules are detected by imaging studies done for other reasons. These nodules are termed incidental nodules, as they are not related to the reason the study was ordered. One such example are Positron Emission Tomography/Computed Tomography (PET/CT) scans that are done to look for spread of a nonthyroid cancer such as breast cancer or lung cancer. While the CT component of these scans identify the incidental nodule, the PET component of these scans determine the activity of the nodule identified. PET/ CT scans are helpful as cancer is usually PET-positive. However, some benign thyroid nodules may also be PET-positive. Overall, incidental thyroid nodules are found in 2% of PET/CT scans. Of these, up to 30% may be thyroid cancer, the vast majority of which are small thyroid cancers.

This study was done to look at the impact of pursuing workup and treatment of incidental thyroid nodules that are found on PET/CT scans. The goal of this study is to provide guidance regarding the appropriate management of incidental thyroid nodules discovered by PET/CT scans performed for evaluation of nonthyroid cancers.

THE FULL ARTICLE TITLE
Piek MW et al 2021 Retrospective analyses of 18FDG-PET/CT thyroid incidentaloma in adults: Incidence, treatment, and outcome in a tertiary cancer referral center. Thyroid 31:1715–1722. PMID: 34340567.

SUMMARY OF THE STUDY
This study included all patients who underwent PET scans for suspected or known nonthyroid cancer between January 2010 and January 2020 in a cancer center in the Netherlands (a total of 52,593 patients). They screened the reports for those who mentioned a thyroid abnormality and excluded anyone who had a previously known thyroid disease. They looked at the patients that had PET-positive nodules and what further workup was done (including thyroid ultrasound, thyroid biopsy and surgery) as well as the patient.

They found that 1.9% of individuals undergoing a PET/ CT imaging had PET-positive incidental thyroid nodules (a total of 1003 patients). The average age of these patients was about 74 years old and most were women (72%). They were able to obtain follow up information on 800 of these patients and found that 42% died during the study period, of which only 1 patient died of thyroid cancer. The incidental thyroid nodules led to 337 ultrasounds, 259 biopsies and 6% of those patients had thyroid surgery. They noticed that the patient survival had nothing to do with the thyroid nodule even if it was a thyroid cancer. Not surprising, survival was dependent on the nonthyroid cancer that led to the PET/CT Scan. After statistical analysis, they determined that there was no survival benefit for patients who underwent evaluation of the incidental thyroid nodules found by PET/CT scans done for nonthyroid cancer

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study concluded that the workup of incidental thyroid nodules noticed on PET/CT scans should depend on the survival expectation of the nonthyroid cancer. It puts into perspective that many patients will undergo unnecessary tests with the anxiety that can come from having a possible second cancer diagnosis with no significant benefit to their quality of life or life expectancy. This study suggests that physicians and patients should have a thorough conversation prior to proceeding with an evaluation of an incidental thyroid nodule to determine if it is an appropriate decision.

— Maria Brito, MD

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