Are Flame Retardants Driving Some of Thyroid Cancer Increase?

April 01, 2017

Initial research suggests that some flame retardants, used in many furnishings in the home, could be associated with an increased risk of papillary thyroid cancer, the most common form of this type of cancer.

Reporting the findings at the ENDO 2017: The Endocrine Society Annual Meeting today, Julie Ann Sosa, MD, of Duke University Medical Center, Durham, North Carolina, said: "What's really novel about this study is that it's the first time we've seen a signal like this, but it should just be seen as a first study. We really need to do additional research, to understand mechanisms…and to validate our findings."

Nevertheless, the results are important, said Dr Sosa, an endocrine surgeon and surgical oncologist, given that papillary thyroid cancer is the fastest increasing cancer in the United States and many other countries.

"There is a pandemic of thyroid cancer around the world," Dr Sosa told a press briefing here. "For too long, we've ascribed this to entirely to overdiagnosis, so we are restricting screening," and studies like this "suggest we should be redirected to understanding what additional causative factors are at play."

Indeed, new data from her group, published only yesterday in the Journal of the American Medical Association, show an increased incidence of thyroid cancer, particularly papillary thyroid cancer, and also ― for the first time ― an increase in cancer-specific mortality, which they believe is a real phenomenon.

This latest study indicates that "potentially we should be emphasizing prevention as much as we are currently emphasizing treatment," she stressed.

Dr Sosa's work also showed that different chemicals appeared to be linked to different types of tumors.

"We saw that three flame retardants have some sort of association with papillary thyroid cancer, but they are very different. One is a brominated flame retardant and the other two are organophosphate flame retardants. They are also very different in terms of where they are located in the home and in your life. This difference begs for more interrogation."

House Dust Analyzed for Flame Retardants in Case-Control Study

Dr Sosa and colleagues recruited 140 participants for their study, 70 of whom had papillary thyroid cancer (cases) while 70 were age- and gender-matched controls without any history of thyroid cancer. Almost 80% of all participants were women, reflecting the gender imbalance found in this type of cancer.

The study was novel in that researchers collected and analyzed house dust from the participants' homes as a measure of exposure to flame retardants — levels of the latter in house dust significantly correlate with personal exposure, Dr Sosa explained. Participants had, on average, lived in their homes for 11 years.

Levels of some flame retardants were higher in the homes of papillary thyroid cancer cases.

One brominated flame retardant, BDE-209, found in electronic casing and upholstery, which was phased out in 2013, appeared to be associated with increases in the smallest, least aggressive type of papillary thyroid cancer — the very type of cancer for which increases have been attributed to overscreening. Those with dust BDE-209 concentrations above the median were 2.29 times as likely to have papillary thyroid cancer as compared with those with low BDE-209 concentrations.

Meanwhile two other very different compounds, TCEP and TPHP, organophosphate flame retardants found in plastic and upholstered furniture frames, were associated with larger, more aggressive papillary thyroid tumors that extended beyond the thyroid.

For example, participants with house-dust TCEP levels above the median were 4.14 times more likely to have cancer with extrathyroidal extension but were not significantly more likely to have it without extrathyroidal extension

What Should Doctors Do With This?

Commenting on what clinicians should take from this research and other studies on the potential harms of endocrine-disrupting chemicals, Dr Sosa said: "With flame retardants, for some time there has been awareness of the value that they bring — protecting from flammability and meeting very important [safety] standards — but that has potentially come at a cost that these flame retardants might have on human health, on human cancers."

"The challenge is…if we understand what the cons are of many of these chemicals, then we can start to work on developing alternatives that do not potentially have this effect.

"As a clinician, it's thinking about what role screening plays, but also taking a more detailed fastidious history and physical examination to try to better tease out what our patients do in all phases of their life, instead of potentially asking a historical set of questions that are no longer contemporary."

Asked for her thoughts, Lindsey Trevino, PhD, who presented her own findings on early life exposure to BPA affecting subsequent risk of fatty-liver disease, said: "As a basic researcher, I don't see patients, but I'm hoping that some of the results of these studies lead to better awareness for physicians and for patients that these are the things that we need to start thinking about.

"Because, for example with fatty liver, it's not just bad diet, it's not just lack of exercise, but now more and more studies are showing that it's these environmental exposures that also play a big role. It's about getting the word out and being aware, and then we can go from there to do some more studies."

Dr Sosa is a member of the data monitoring committee for the Medullary Thyroid Cancer Consortium Registry and has relationships with Novo Nordisk, AstraZeneca, GlaxoSmithKline, and Eli Lilly. Disclosures for the coauthors are listed in the abstract.

Follow Lisa Nainggolan on Twitter: @lisanainggolan1 . For more diabetes and endocrinology news, follow us on Twitter and on Facebook.

ENDO 2017. April 1, 2017; Orlando, Florida. Abstract SAT-248



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