The study, published last week in the Journal of Clinical Oncology, found that women with the highest concentrations of two chemicals known as PFOA and PFOS had higher rates of estrogen receptor-negative breast cancer, a subtype that tends to be more aggressive and more difficult to treat than other forms of the disease.

Women with the highest levels of PFOA had a 67 percent higher rate of this type of breast cancer compared with women who had the lowest levels, according to the NIH. For PFOS, the rate was 93 percent higher.

The findings add to a growing body of evidence about the health risks posed by per- and polyfluoroalkyl substances, a sprawling class of synthetic chemicals used for decades in products ranging from nonstick cookware and water-resistant clothing to firefighting foam and food packaging. The compounds are nicknamed "forever chemicals" because they do not readily break down in the environment or in the human body, and they have been detected in drinking water supplies and in the blood of people across the country.

The new analysis focused specifically on estrogen receptor-negative breast cancer, a category that includes triple-negative breast cancer and other subtypes that lack hormone receptors and therefore do not respond to treatments that target estrogen or progesterone. These cancers generally have fewer treatment options and worse outcomes than hormone-receptor-positive tumors.

The research does not establish that the chemicals cause the cancer, but it strengthens the case for reducing exposure, particularly for women who may already be at elevated risk. The NIH said the study adds to the understanding of how environmental exposures may influence cancer risk.

PFAS contamination has become a pressing concern in communities nationwide, including in Massachusetts, where regulators and local officials have grappled with contaminated water supplies and calls for stricter limits on the chemicals. The Environmental Protection Agency has moved in recent years to regulate several PFAS compounds in drinking water, a step that public health advocates have welcomed while arguing that more needs to be done to clean up legacy contamination and to hold manufacturers accountable.

The study's authors and outside experts have emphasized that people can reduce their exposure by using water filters certified to remove PFAS, avoiding certain nonstick and stain-resistant products, and supporting efforts to clean up contaminated water sources. But they also note that individual behavior changes cannot fully address a problem rooted in widespread environmental contamination.

The findings were published in the Journal of Clinical Oncology and announced by the NIH.