Air pollution could increase breast cancer risk: study

Traffic-related air pollution may put women at risk for breast cancer, according to a new study from Quebec.

The study, published in the journal Environmental Health Perspectives, looks at links between the risk of breast cancer, a leading cause of death from cancer in women, and traffic pollution.

Researchers from McGill University and the Université de Montréal charted incidences of breast cancer and compared them with pollution maps.

“We’ve been watching breast cancer rates go up for some time,” study co-author Mark Goldberg, a researcher at McGill University Health Centre, said in a release on Wednesday.

“Nobody really knows why, and only about one-third of cases are attributable to known risk factors. Since no one had studied the connection between air pollution and breast cancer using detailed air pollution maps, we decided to investigate it.”

Dr. Goldberg and his colleagues combined data from several studies. They created two air pollution maps which showed levels of nitrogen dioxide, a byproduct of vehicle traffic, in different parts of Montreal in 1996 and 10 years earlier in 1986.

Then, the research team looked at the home addresses of women diagnosed with breast cancer in a 1996-97 study and charted that onto the air pollution maps.

The team says its results were “startling,” and showed the incidence of breast cancer was increased in areas with higher levels of air pollution.

“We found a link between post-menopausal breast cancer and exposure to nitrogen dioxide (NOsub2/sub), which is a marker for traffic-related air pollution,” Dr. Goldberg said in the release.

“Across Montreal, levels of NOsub2/sub varied between five parts per billion to over 30 parts per billion. We found that risk increased by about 25% with every increase of NOsub2/sub of five parts per billion.

“Another way of saying this is that women living in the areas with the highest levels of pollution were almost twice as likely to develop breast cancer as those living in the least polluted areas.”

Dr. Goldberg warns, however, that the study must be interpreted with caution.

“First of all, this doesn’t mean NOsub2/sub causes breast cancer,” he said. “This gas is not the only pollutant created by cars and trucks, but where it is present, so are the other gases, particles and compounds we associate with traffic — some of which are known carcinogens.”

Dr. Goldberg said the study can be subject to unknown variables and that some areas of uncertainty remain.

“For example, we don’t know how much the women in the study were exposed to pollution while at home or at work, because that would depend on their daily patterns of activity, how much time they spend outdoors and so on,” Dr. Goldberg said.

“At the moment, we are not in a position to say with assurance that air pollution causes breast cancer. However, we can say that the possible link merits serious investigation,” the team said in its release.

Studies published in the U.S, have also shown possible links between cancer and air pollution.

The study was funded by a research grant from the Canadian Cancer Society and another one from the Canadian Institutes of Health Research.

Stem Cell 'Daughters' Lead To Breast Cancer

Walter and Eliza Hall Institute scientists have found that a population of breast cells called luminal progenitor cells are likely to be responsible for breast cancers that develop in women carrying mutations in the gene BRCA1.

BRCA1 gene mutations are found in 10-20 per cent of women with hereditary breast cancer. Women with BRCA1 mutations often develop 'basal-like' breast cancer, which is a particularly aggressive form of the disease.

A team led by Associate Professors Jane Visvader and Geoff Lindeman from the institute's Victorian Breast Cancer Research Consortium Laboratory have discovered that luminal progenitor cells – the 'daughters' of breast stem cells – are the likely source of basal-like breast tumours. Their finding, published in today's issue of the international journal Nature Medicine, represents a major shift in the way scientists think breast cancer develops.

Dr Visvader said it had been thought in recent years that breast stem cells gave rise to BRCA1 tumours. "However, research carried out at the institute by Drs Elgene Lim and François Vaillant has shown that breast tissue from women with BRCA1 mutations has unexpectedly high numbers of luminal progenitor cells," she said.

"Further, our gene expression studies have revealed that BRCA1 breast tissue and basal breast tumors are more similar to normal luminal progenitor cells than any other cell type in the breast. This places the spotlight on errant luminal progenitors, rather than breast stem cells."

Dr Lindeman, who also heads the Familial Cancer Centre at the Royal Melbourne Hospital, said that now the importance of luminal progenitor cells in breast cancer was known it opened the way for the development of new drugs or therapies to treat breast cancer, one of the biggest causes of premature death in women.

"BRCA1 women have approximately a 65 per cent lifetime chance of developing breast cancer. Following surgery, treatment options available to these women are often limited to chemotherapy and radiotherapy, so identifying new treatment and prevention strategies is a priority for us," he said.

Luminal progenitor cells in women with BRCA1 mutations have 'forgotten' how to behave, Dr Lindeman said. "Usually, luminal progenitor cells multiply rapidly in the presence of certain growth factors. In BRCA1 women these cells don't even require growth factors to proliferate – they misbehave from the outset. "We also know that the BRCA1 gene is required for normal DNA repair. There may therefore be a triple whammy effect – faulty growth control, faulty DNA repair and expanded luminal progenitor cell numbers –ultimately resulting in breast cancer in some BRCA1 mutation carriers."

Dr Visvader said in the long-term, breast biopsies might be able to reveal misbehaving luminal progenitor cells. What's more, certain 'markers' might one day help guide diagnosis and treatment. "For example, c-KIT is a key marker of the luminal progenitor cell and I expect we will see an increase in pathologists routinely using this as a diagnostic marker for basal-like tumours," she said. "It may even be possible to develop new drugs that target c-KIT, since drugs are already available that target different forms of this marker."

Dr Lindeman said the identification of stem cells, luminal progenitor cells and other cell types in the breast was now beginning to reveal a breast cancer roadmap - highlighting cancer-prone cell types and key genetic pathways. "Hopefully this will lead to new, tailored therapies for the next generation of women."

Dr Visvader said the research had only been possible through the generous donation of breast tissue by women undergoing breast surgery, together with the support of their surgeons and pathologists. The study was facilitated by the Kathleen Cuningham Foundation Consortium for Research into Familial Breast Cancer.

The research was supported by the Victorian Breast Cancer Research Consortium, the Susan G. Komen Foundation, the National Breast Cancer Foundation, the National Health and Medical Research Council, the Australian Stem Cell Centre, the US Department of Defense and the Australian Cancer Research Foundation.