Duke: Higher exposure to chemicals used to reduce the flammability of
furniture, carpets, electronics and other household items appears to be
associated with papillary thyroid cancer, according to study conducted
by the Duke Cancer Institute and the Nicholas School of the Environment at Duke University. Reporting April 1 at the ENDO 2017 meeting in Orlando, the Duke
research team found a significant association between higher levels of
certain flame retardants in household dust and being a patient with
papillary thyroid cancer, which is increasing at the fastest rate of any
cancer in the United States.
“The incidence of papillary thyroid cancer has risen an average of 7
percent a year in the United States for the last two decades,” said
co-senior author Julie Ann Sosa,
M.D., chief of endocrine surgery at the Duke Cancer Institute. “At the
same time, exposure to flame retardant chemicals has also increased.
“These chemicals are known as endocrine disruptors, and specifically
they affect thyroid function,” Sosa said. “We know that some flame
retardants share a similar chemical structure with thyroid hormones, and
there has been quite a bit of interest around their impact on thyroid
regulation and clinically significant thyroid disease. Our study was
designed to explore whether there is an association between these
chemicals and having thyroid cancer.”
Sosa and co-senior author Heather M. Stapleton,
Ph.D., associate professor of Environmental Chemistry and Exposure
Science at the Nicholas School of the Environment, led an
interdisciplinary team that studied 140 patients with and without
papillary thyroid cancer. The patients had lived in their homes for an
average of 11 years, providing a population with long-term exposures in
the home that could be characterized by analyzing home dust samples.
The researchers collected household dust to measure flame retardants
in the home environment. They also analyzed the participants’ blood,
focusing on biomarkers for one class of flame retardants, polybrominated
diphenyl ethers (PBDE), which were once the most common chemicals used
to inhibit flammability in furniture until they were phased out in the
2000s because of toxicity and human health concerns.
“Despite declining use, PBDE chemicals are still detected in indoor
dust samples because many people still have treated products in their
home -- for example, things like sofas or TVs,” Stapleton said. “Flame
retardants readily leach from the products over time. The Environmental
Protection Agency estimates that 80 percent of the U.S. population’s
exposure to PBDE flame retardants is from indoor dust.”
Accounting for other risk factors for papillary thyroid cancer, the
researchers identified several important associations between long-term
flame retardant exposures and the odds of having papillary thyroid
cancer, particularly with respect to increased tumor aggressiveness.
Exposures to two particular chemicals -- decabromodiphenyl ether
(BDE-209) and tris(2-chloroethyl) phosphate (TCEP) in dust – were most
strongly associated with higher odds of having papillary thyroid cancer
incidence.
Study participants with elevated concentrations of BDE-209 in dust
were 2.3 times as likely to have thyroid cancer than those with low
concentrations. TCEP in dust was more strongly associated with larger,
more aggressive tumors. In contrast, patients with the highest levels of
BDE-209 in dust had less aggressive tumors.
“Taken together, these results suggest exposure to several flame
retardants may be associated with the diagnosis and severity of
papillary thyroid cancer, potentially explaining some of the observed
‘epidemic’ in the incidence of this disease,” Stapleton said. “Next
efforts should include replicating these results in a different, larger
cohort of patients and understanding what the underlying mechanisms are
that support these observations.”
“With the incidence of thyroid cancer quickly increasing and little
knowledge of what may be leading to this drastic increase, it is of
critical importance to understand potential environmental factors that
might be contributing,” Sosa added.
In addition to Sosa and Stapleton, study authors include Kate
Hoffman, Amelia Lorenzo, Craig M. Butt, Stephanie C. Hammel, Brittany
Bohinc Henderson, Sanziana A. Roman, and Randall P. Scheri.
The study received funding support from Fred & Alice Stanback,
the Duke Cancer Institute, and the Nicholas School of the Environment.