Carried out by researchers at the University of Massachusetts Amherst, the new study is the largest to date on the relationship between phthalates and breast cancer, and is the first to measure phthalate exposure before a cancer diagnosis.
Measuring phthalates after a diagnosis could show exposure from medical equipment or medication, rather than exposure from contact with everyday products before developing cancer.
Data was gathered from the Women Health Initiative (WHI), a long-term national health study which includes more than 160,000 postmenopausal women.
The researchers examined levels of 11 phthalate metabolites in urine samples taken from 419 women who were diagnosed with invasive breast cancer after Year 3 of the WHI, and from 838 healthy women who didn’t develop breast cancer.
The findings, published in the Journal of the National Cancer Institute, failed to show an association between phthalates and breast cancer, with the researchers adding that it “rules out any extreme increase in risk.”
However, the question is still open as to whether there is some relationship between phthalate exposure and breast cancer, according to lead author Katherine Reeves.
“Our research has raised almost as many questions as it’s answered,” outlined Reeves. “I think this is an important contribution to the literature, but there’s still a lot more work to be done, including looking at younger women.”
Reeves added, “The most critical time for breast cancer development is in previous years. Looking at women in their 50s and 60s may not be the most important exposure period.”
A strong point of the study is that the researchers tested several urine samples from each participant every few years, which can increase accuracy, as half of phthalate metabolites are excreted in urine within 12 to 24 hours of exposure.
“If you’re relying on a single measurement, you may be misclassifying people and either getting no association or the wrong association,” said Reeves.
However, the researchers acknowledge that the study still had its limitations.
“People’s phthalate exposure changes quite a bit over time, and this makes it challenging to characterize the people who are the most exposed and who are the least, which is what we need to be able to do in order to evaluate whether higher phthalate exposure is related to breast cancer risk,” Reeves said.
“Using two to three samples per person helped, but it wasn’t fully able to overcome that challenge.”
“We need to know the answer about whether or not these chemicals are causing breast cancer or other health outcomes,” Reeves said. “It’s a pressing issue and we’re trying to think of creative approaches to get not just an answer, but the right answer.”