Increase in Papillary Thyroid Cancer Incidence Is Accompanied by Changes in the Frequency of theBRAFV600EMutation: A Single-Institution Study

In recent years, the T1799A B-type Raf kinase (BRAF) mutation in thyroid cancer has received enthusiastic investigation, and significant progress has been made toward understanding its tumorigenic role and clinical significance. Among various thyroid tumors, this mutation occurs uniquely in papillary thyroid cancer (PTC), the most common endocrine malignancy, and some apparently PTC-derived anaplastic thyroid cancers. Many studies have found this mutation to be associated with those clinicopathological characteristics of PTC that are conventionally known to predict tumor progression and recurrence, including, for example, old patient age, extrathyroidal invasion, lymph node metastasis, and advanced tumor stages. Direct association of BRAF mutation with the clinical progression, recurrence, and treatment failure of PTC has also been demonstrated. The BRAF mutation has even been correlated with PTC recurrence in patients with conventionally low-risk clinicopathological factors. Some molecular mechanisms determining BRAF mutation-promoted progression and the aggressiveness of PTC have recently been uncovered. These include the down-regulation of major tumor suppressor genes and thyroid iodide-metabolizing genes and the up-regulation of cancer-promoting molecules, such as vascular endothelial growth factor, matrix metalloproteinases, nuclear transcription factor kappaB, and c-Met. Thus, BRAF mutation represents a novel indicator of the progression and aggressiveness of PTC. Significant advances have also occurred in the preclinical testing of new therapeutic strategies targeting the MAPK pathway aberrantly activated by BRAF mutation and other related mutations. New mitogen extracellular kinase (MEK) inhibitors developed recently are particularly promising therapeutic agents for thyroid cancer. With these advances, it has become clearer that BRAF mutation will likely have significant impact on the clinical management of PTC.

Use of BRAF mutation in papillary thyroid cancer (PTC) has the potential to improve risk stratification of this cancer. The objective of the study was to investigate the prognostic value of BRAF mutation in patients with PTC. In a multicenter study of 219 PTC patients, data on their clinicopathological characteristics and clinical courses between 1990 and 2004 were retrospectively collected, and their tumor BRAF mutation status was determined. Associations of BRAF mutation with initial tumor characteristics and subsequent recurrence were analyzed. Relationships between the BRAF mutation status and clinicopathological outcomes, including recurrence, were measured. We found a significant association between BRAF mutation and extrathyroidal invasion (P < 0.001), lymph node metastasis (P < 0.001), and advanced tumor stage III/IV (P = 0.007) at initial surgery. This association remained significant on multivariate analysis, adjusting for conventional clinicopathological predictors of recurrence excluding the histological PTC subtype, but was lost when the tumor subtype was included in the model. BRAF mutation was also significantly associated with tumor recurrence, 25 vs. 9% with and without mutation, respectively (P = 0.004), during a median of 15 (interquartile range, 3-29) months of follow-up. This association remained significant on multivariate analysis adjusting for conventional clinicopathological predictors of recurrence, even including the PTC subtype (odds ratio, 4.0; 95% confidence interval, 1.1-14.1; P = 0.03). BRAF mutation was even an independent predictor of recurrence in patients with stage I/II disease, 22 vs. 5% with and without BRAF mutation, respectively (P = 0.002). BRAF mutation was also more frequently associated with absence of tumor I-131 avidity and treatment failure of recurrent disease. In patients with PTC, BRAF mutation is associated with poorer clinicopathological outcomes and independently predicts recurrence. Therefore, BRAF mutation may be a useful molecular marker to assist in risk stratification for patients with PTC.

The rapidly rising incidence of papillary thyroid cancer may be due to overdiagnosis of a reservoir of subclinical disease. To conclude that overdiagnosis is occurring, evidence for an association between access to health care and the incidence of cancer is necessary. We used Surveillance, Epidemiology, and End Results (SEER) data to examine U.S. papillary thyroid cancer incidence trends in Medicare-age and non-Medicare-age cohorts over three decades. We performed an ecologic analysis across 497 U.S. counties, examining the association of nine county-level socioeconomic markers of health care access and the incidence of papillary thyroid cancer. Papillary thyroid cancer incidence is rising most rapidly in Americans over age 65 years (annual percentage change, 8.8%), who have broad health insurance coverage through Medicare. Among those under 65, in whom health insurance coverage is not universal, the rate of increase has been slower (annual percentage change, 6.4%). Over three decades, the mortality rate from thyroid cancer has not changed. Across U.S. counties, incidence ranged widely, from 0 to 29.7 per 100,000. County papillary thyroid cancer incidence was significantly correlated with all nine sociodemographic markers of health care access: it was positively correlated with rates of college education, white-collar employment, and family income; and negatively correlated with the percentage of residents who were uninsured, in poverty, unemployed, of nonwhite ethnicity, non-English speaking, and lacking high school education. Markers for higher levels of health care access, both sociodemographic and age-based, are associated with higher papillary thyroid cancer incidence rates. More papillary thyroid cancers are diagnosed among populations with wider access to healthcare. Despite the threefold increase in incidence over three decades, the mortality rate remains unchanged. Together with the large subclinical reservoir of occult papillary thyroid cancers, these data provide supportive evidence for the widespread overdiagnosis of this entity.