ORLANDO –with incidence-based mortality increasing by 1.1% annually from 1994 to 2013, according to a study conducted by the National Cancer Institute.
In a study of 77,726 patients diagnosed with thyroid cancer between 1974 and 2013, incidence rates increased from 4.56 per 100,000 person-years during 1974-1977 to 14.42 per 100,000 person-years during 2010-2013, according to Hyeyeun Lim, PhD, a postdoctoral fellow at National Cancer Institute, and colleagues ().
A majority of patients in the sample were female (75%) and white (82%); average age was 48 years.
A notable trend was the increase in papillary thyroid cancer (PTC). PTC was the most common thyroid cancer at 83.6% of diagnoses, followed by follicular, medullary, anaplastic, and other at 10.8%, 2.2%, 1.3%, and 2.1%, respectively. PTC was associated with the highest annual percent change (4.4%) and the only positive incidence-based mortality annual percent change (1.7%) among all histologic types, according to the researchers.
Regional and distant tumors accounted for 53.2% and 29% of deaths, respectively, compared to 13.5% for local tumors.
Dr. Lim and colleagues interpret the increase in incidence to contradict a common idea among researchers that attributes rising rates to new methods of detection such as ultrasound imaging and fine-needle aspiration biopsies.
“Such changes could account for the rapid increases in the incidence rates for localized and small PTCs that have been previously observed,” the researchers reported. “However, the significant, albeit less-rapid increase in advanced-stage and larger PTC incidence rates and increasing thyroid cancer mortality rates among patients diagnosed with advanced-stage PTC is not consistent with the notion that over-diagnosis is solely responsible for the changing trends in PTC incidence.”
While the researchers reported increased mortality rates among all PTC demographics, statistical significance was found solely in patients with distant disease (annual percentage changes, 2.9% [95% confidence interval, 1.1%-4.7%]), stage IV disease (APC, 12.9%[95%CI, 7.2%-19.0%]), or both, according to researchers.
Researchers speculate increased rates of obesity, childhood ionizing radiation exposure, and increased exposure to pesticides may be possible sources for increased rates of PTC, however Dr. Lim and peers assert further research must be conducted.
Based on these findings, researchers suggest “renewed focus on aggressive transdisciplinary management that includes surgery, adjuvant radioactive iodine, and, when indicated for the 5%-10% of patients who develop progressive disease, systemic therapy,” for patients with advanced-stage PTC.
Due to the nature of the study, researchers were limited to speculating potential reasons for increase in thyroid cancer incidence. Information of tumor size and stage was limited to the years when this information began to be recorded, after the initial years included in the study.