A 22-year study of more than 10,000 French women found that the risk of breast cancer increased when they were exposed to more benzo[a]pyrene, an air pollutant mostly produced in residential burning, despite nearly all of the subjects living in areas where its concentration was below levels the European Union deems to be safe.

Publishing their results in Environment International in January, the researchers found that the risk of breast cancer increased by about 15% for every increase of 1.42 nanograms per cubic meter in benzo[a]pyrene exposure — though few subjects were exposed to more than the EU limit of 1 nanogram per cubic meter. The correlation was even higher for women who were in early menopause and who smoked tobacco.

The authors also discovered stronger links to breast cancers with estrogen or progesterone receptors and to those categorized as grade 3, which are the most aggressive and spread quickly.

Benzo[a]pyrene, or BaP, is mostly produced by residential burning of wood and coal, although other sources include tobacco smoke, vehicle emissions and industrial activity. The air pollutant is a labeled carcinogen that causes lung and other cancers, but its link to breast cancer in humans had not been studied before at a large scale.

France experiences the fourth-highest rate of breast cancer in the world and had more than 58,000 new cases in 2020. The same year, breast cancer became the most commonly diagnosed form of cancer in both sexes, with about 2.3 million new cases worldwide.

The BaP project was led by Béatrice Fervers, a trained oncologist at French cancer hospital Centre Léon Bérard. She noted that her team’s findings need to be confirmed in future studies but that they align with previous research on BaP’s effects on breast cancer.

“This is an interesting finding that’s not been much investigated in the literature,” said Fervers, who is also a professor of medicine at Lyons University.

The study analyzed 5,222 French women who developed cancer and another 5,222 women selected as matched controls. They were chosen from a 22-year-long preexisting project that has been tracking nearly 100,000 French women, and the researchers could determine their BaP exposure from ambient air based on their locations.

Because the long-term study was designed to investigate cancers, the researchers had the data to adjust for a wide array of relevant factors, Fervers said, such as family history, oral contraception use, physical activity and pregnancies. The dataset included only teachers and other school workers to avoid occupational bias in the results, she said.

The findings also appear to demonstrate that the EU’s air standards for BaP may be too high to avoid rises in breast-cancer incidence. Only 0.2% of study participants were exposed to concentrations above the annual target value for BaP of 1 nanogram per cubic meter, yet the researchers were still able to detect a significant increased risk from the study.

“This of course questions the targeted values,” Fervers said.

The World Health Organization does not provide a safe limit for BaP because it is a carcinogen, but one group of scientists proposed that 0.12 nanograms per cubic meter — less than one-eighth of the EU limit — would enforce an “acceptable risk level.” A full 77% of study participants experienced levels above this strict proposed standard.

Fervers is involved in numerous ongoing breast-cancer studies that are investigating BaP exposure from food and commuting as well as the effects of seven other air pollutants, and whether the risk compounds when people are exposed to many of them. She is also working on creating an estimate for the number of breast cancer deaths attributable to BaP exposure in France, which she said could inform public health policies.

The article, "Risk of breast cancer associated with long-term exposure to benzo[a]pyrene 9BaP) air pollution: Evidence from the French E3N cohort study," was published Jan. 24 in Environment International. The authors of the study were Amina Amadou, Delphine Praud, Floriane Dygas, Leny Grassot and Béatrice Fervers, Centre Léon Bérard and Inserm U1096; Thomas Coudon, Centre Léon Bérard, Inserm U1096 and Claude Bernard University Lyon 1; Pietro Salizzoni, Claude Bernard University Lyon 1; Elodie Faure, Centre Léon Bérard and Paris-Saclay University; Francesca Romana Manchini, Paris-Saclay University; Florian Couvidat and Julien Caudeville, National Institute for Industrial Environment and Risks; Bertrand Bessagnet, National Institute for Industrial Environment and Risks and Technical Reference Center for Air Pollution and Climate Change; John Gulliver, Centre for Environmental Health and Sustainability; Karen Leffondré, University of Bordeaux; and Gianluca Severi, Paris-Saclay University and University of Florence, Italy. The lead author was Béatrice Fervers.