By the way, industry is fond of saying that PAHs can be found anywhere and that there are more PAHs in a grilled hamburger than in coal tar pavement sealants. Not even close. Actually the New York Academy of Sciences said in their landmark study in 2007 that a typical charbroiled burger has a concentration of 2.2 mg/kg of PAH. While the exposure pathways are different, the concentration of coal tar sealants is over 30,000 times more than a charbroiled burger!
What research has been done on the connection to PAHs and breast cancer? I found a great summary report by the Breast Cancer Fund (who also supported the ban of coal tar sealants in California). The title of the report is "The State of the Evidence 2010: The Connection Between Breast Cancer and the Environment."
PAH Cancer Producing Potential Explained
Like many other environmental chemicals that are associated with breast cancer risk, PAHs are lipophilic and are stored in the fat tissue of the breast. PAHs have been shown to increase risk for breast cancer through a variety of mechanisms. The most common PAHs are weakly estrogenic (estrogen mimicking), due to interactions with the cellular estrogen receptor (Pliskova, 2005). However, the major receptor directed pathway is different, with PAHs associating with a protein called the aryl hydrocarbon receptor (AhR), initiating a series of cell changes that lead to altered cell signaling and ultimately to increases in DNA mutations (Kemp, 2006; Santodonato, 1997). PAHs can also be directly genotoxic, meaning that the chemicals themselves or their breakdown products can directly interact with genes and cause damage to DNA (Ralston, 1997). Several epidemiological studies have implicated PAH exposure in increased risk for breast cancer (p.45).
Long Island Study Finds Correlation of PAH-damaged DNA (aka "adducts") and Breast Cancer
One of the studies from the Long Island Breast Cancer Study Project found that women with the highest level of PAH-DNA adducts had a 50 percent increased risk of breast cancer. PAH-DNA adducts are indicators of problems in DNA repair in cells, one of the early hallmarks of tumor development (Gammon, 2002). In an earlier report, researchers explored the presence of PAH-DNA adducts in breast samples taken from women diagnosed with cancer as compared with those diagnosed with benign breast disease. Cancerous samples were twice as likely to have PAH-DNA adducts as were benign samples (Rundle, 2000). Followup work indicates that those women who had higher levels of PAH adducts may not necessarily have had higher exposures to PAHs, but instead had particular genetic profiles that encourage the deficits in DNA repair (Gammon, 2008). Other studies support the presence of different genetic profiles for women who have increased numbers of PAH-DNA adducts, including polymorphisms in genes involved in cell metabolism, tumor-suppressor mechanisms and DNA repair (Gammon, 2008; Mahadevan, 2005). Differences were not found in the profiles of genes whose products are involved in the activation and deactivation of the PAHs themselves (McCarty, 2009) (p.45).
PAH Exposure at the Time of Birth Correlates with Future Breast Cancer Risk
There is one human study that has more directly examined the connection between environmental exposures around the time of birth and later development of breast cancer. A study from western New York examined air monitoring records from 1959 to 1997 to establish polycyclic aromatic hydrocarbon (PAH) levels in residential areas. PAHs are products of incineration found in air pollution, vehicle exhaust (particularly diesel), tobacco smoke and grilled foods. They have been shown to be carcinogenic and to increase risk for breast cancer by altering a number of hormone mediated systems (Kemp, 2006; Santodonato, 1997). This case control study of 3,200 women (ages 35 to 79) showed that exposures to high levels of PAHs at the time of birth were associated with an increased risk of postmenopausal breast cancer decades later (Bonner, 2005) (p.20).
So there is a strong link between PAHs and coal tar, as well as PAHs and breast cancer. Perhaps the byline of the Breast Cancer Fund is an appropriate close to this post:
Help us expose and eliminate the environmental causes of breast cancer. Together we can stop this disease before it starts.
Later this week I will be participating with a group of high school classmates in a breast cancer fundraising walk/run. I hope to report more on that later.