The incidence of detected thyroid cancer cases has been increasing in the United States since 1975. The majority of thyroid cancers are differentiated cancers with excellent prognosis and long-term survival.Objective
To systematically review the benefits and harms associated with thyroid cancer screening and treatment of early thyroid cancer in asymptomatic adults to inform the US Preventive Services Task Force.Data Sources
Searches of MEDLINE, PubMed, and the Cochrane Central Register of Controlled Trials for relevant studies published from January 1966 through January 2016, with active surveillance through December 2016.Study Selection
English-language studies conducted in asymptomatic adult populations.Data Extraction and Synthesis
Two reviewers independently appraised the articles and extracted relevant study data from fair- or good-quality studies. Random-effects meta-analyses were conducted to pool surgical harms.Main Outcomes and Measures
Thyroid cancer morbidity and mortality, test accuracy to detect thyroid nodules or thyroid cancer, and harms resulting from screening (including overdiagnosis) or treatment of thyroid cancer.Results
Of 10 424 abstracts, 707 full-text articles were reviewed, and 67 studies were included for this review. No fair- to good-quality studies directly examined the benefit of thyroid cancer screening. In 2 studies (n = 354), neck palpation was not sensitive to detect thyroid nodules. In 2 methodologically limited studies (n = 243), a combination of selected high-risk sonographic features was specific for thyroid malignancy. Three studies (n = 5894) directly addressed the harms of thyroid cancer screening, none of which suggested any serious harms from screening or ultrasound-guided fine-needle aspiration. No screening studies directly examined the risk of overdiagnosis. Two observational studies (n = 39 211) included cohorts of persons treated for well-differentiated thyroid cancer and persons with no surgery or surveillance; however, these studies did not adjust for confounders and therefore were not designed to determine if earlier or immediate treatment vs delayed or no surgical treatment improves patient outcomes. Based on 36 studies (n = 43 295), the 95% CI for the rate of surgical harm was 2.12 to 5.93 cases of permanent hypoparathyroidism per 100 thyroidectomies and 0.99 to 2.13 cases of recurrent laryngeal nerve palsy per 100 operations. Based on 16 studies (n = 291 796), 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.Conclusions and Relevance
Although ultrasonography of the neck using high-risk sonographic characteristics plus follow-up cytology from fine-needle aspiration can identify thyroid cancers, it is unclear if population-based or targeted screening can decrease mortality rates or improve important patient health outcomes. Screening that results in the identification of indolent thyroid cancers, and treatment of these overdiagnosed cancers, may increase the risk of patient harms.