Thyroid cancer has been reported to be the fastest increasing cancer diagnosis in the United States. A new study says the annual growth in thyroid cancer incidence tripled between 1975 and 2013, with a majority of the new diagnoses being papillary thyroid cancer.
In recent years, epidemiologists have been attributing the surge in thyroid cancer to the broad detection of more cases. With advanced tools like fine-needle biopsies and ultrasound systems, doctors are now better equipped to diagnose thyroid cancer, including those with slow-growing nonmalignant symptoms.
"While overdiagnosis may be an important component to this observed epidemic, it clearly does not explain the whole story," said Dr. Julie Sosa, co-author and Duke University's head of endocrine surgery.
Thyroid Cancer Rate Increase
From the database of National Cancer Institute, the researchers analyzed more than 77,000 cases of thyroid cancer reported between 1974 and 2013. Analysis showed a tripling of thyroid cancer cases from that period.
From 1994 to 2013, advanced thyroid cancer cases increased 3 percent annually, while the number of deaths increased by nearly 1 percent every year. Sosa said thyroid cancers are showing a marked increase despite the relatively less lethal nature of the disease.
The new study rules out the rising rates of thyroid cancer to an escalation in the detection of more cases, and attributes the increase in thyroid cancer incidence and mortality rates to many factors, including exposure to flame retardants.
The findings have been published in the Journal of the American Medical Association and the paper was presented at the Endocrine Society's meeting in Orlando recently.
Environmental Impact From Flame Retardants
Flame retardants in home products are one of the causative factors of papillary thyroid cancer, according to the study.
Studies have shown that many flame retardants have endocrine-disrupting chemicals that interfere with thyroid homeostasis, so the researchers turned their attention to flame retardants to trace its relationship with papillary thyroid cancer.
"Our study results suggest higher exposure to several flame retardants in the home environment may be associated with the diagnosis and severity of papillary thyroid cancer," Sosa said.
Papillary thyroid cancer is exacerbated by polybrominated diphenyl ethers, which are pollutants present in home products, plastics, foodstuff, and pesticides.
Number Of Americans Affected By Thyroid Cancer
According to the National Cancer Institute, more than 60,000 Americans are diagnosed with thyroid cancer a year. Of these, nearly 75 percent are women and 82 percent are white.
In another study, it was found that among the ethnic groups showing higher vulnerability to thyroid cancer are Hispanics and African Americans.
"Thyroid cancer incidence is leveling off in the United States. Our analysis, however, shows that the trend of deceleration mainly occurred in non-Hispanic Whites and in older populations, whereas the rate of thyroid cancer continuously increased among the young and the Hispanic and black populations," noted lead author Anupam Kotwal.
Obesity Problem And Decreased Smoking Rate
Other reasons behind the increase in thyroid cancer are rising obesity rates and a decreasing number of smokers.
Obese adults in the United States have tripled between 1960 and 2012, with the highest growth in numbers recorded between 1980 and 2010.Another factor aiding the growth of thyroid cancer comes as a surprise - a decline in smoking.
Though smoking threatens the heart and lungs, it is associated with reducing the risk of thyroid cancer by 30 to 40 percent, added the study. However, this shouldn't be taken as a recommendation to smoke in order to prevent thyroid cancer, the researchers warned.
"It's just an interesting association that we see in our data, and it provides some clues to what factors are involved in thyroid cancer development," said NCI epidemiologist Cari Kitahara.
