From the Guidelines
I recommend against routine screening for thyroid cancer in asymptomatic individuals without specific risk factors, and instead suggest a targeted evaluation using neck ultrasound and measurement of calcitonin levels for those at high risk, such as individuals with a family history of medullary thyroid cancer, genetic syndromes like MEN2, or history of radiation exposure to the neck. The most recent and highest quality study, 1, published in 2012, provides guidelines for the diagnosis, treatment, and follow-up of thyroid cancer, and supports this approach. According to these guidelines, thyroid ultrasound (US) supplemented by fine needle aspiration cytology (FNAC) should be used as a first-line diagnostic procedure for detecting and characterizing nodular thyroid disease.
Some key points to consider when evaluating thyroid nodules include:
- Thyroid nodules are frequent, but thyroid cancer is rare, occurring in only 5% of all thyroid nodules 1
- Fine needle aspiration cytology (FNAC) should be performed in any thyroid nodule >1 cm and in those <1 cm if there is any clinical or ultrasonographic suspicion of malignancy 1
- Measurement of serum calcitonin is a reliable tool for the diagnosis of medullary thyroid cancer and should be an integral part of the diagnostic evaluation of thyroid nodules 1
The reason routine screening isn't recommended is that thyroid cancer is relatively uncommon, and widespread screening could lead to overdiagnosis of small, indolent cancers that would never cause symptoms or harm during a person's lifetime, resulting in unnecessary procedures, treatments, and psychological distress 1. If thyroid nodules are found incidentally or through examination, they should be evaluated according to their characteristics with ultrasound and possibly fine needle aspiration if they meet certain size and appearance criteria.
From the Research
Screening Tests for Thyroid Carcinoma
- The recommended screening test for thyroid carcinoma is not clearly defined, but several studies suggest that routine screening is not recommended for asymptomatic adults 2.
- Ultrasound is considered the first-line diagnostic tool for diagnosis of thyroid diseases, but it should not be used as a general screening tool and should be reserved for patients at high risk of thyroid cancer and in the diagnostic management of incidentally discovered thyroid nodules 3.
- Fine-needle aspiration (FNA) may be performed for nodules ≥ 1.0 cm depending on clinical and sonographic risk factors for thyroid cancer, and FNA specimens should be read by an experienced cytopathologist and be reported according to the Bethesda Classification System 4.
- Molecular analysis of indeterminate FNA samples has potential to better discriminate benign from malignant nodules and thus guide management 4.
Harms of Screening
- The harms of thyroid cancer screening include overdiagnosis and overtreatment, which can lead to unnecessary intervention and decreased quality of life 5, 2.
- The USPSTF found inadequate direct evidence on the harms of screening but determined that the overall magnitude of the harms of screening and treatment can be bounded as at least moderate 2.
- Treatment of differentiated thyroid cancer with radioactive iodine is associated with a small increase in risk of second primary malignancies and with increased risk of permanent adverse effects on the salivary gland, such as dry mouth 5.
Recommendations
- The USPSTF recommends against screening for thyroid cancer in asymptomatic adults 2.
- Routine surveillance using thyroglobulin, neck ultrasound, and physical examination for recurrence in differentiated thyroid cancer patients may not be effective in improving patient survival and/or quality of life, and may lead to unnecessary intervention 6.