A yearlong review of environmental causes for breast tumors by a U.S. research institute failed to definitely identify any chemicals, pesticides or consumer products that trigger the most-common cancer in women.
A woman’s lifestyle, including whether she smokes, drinks or gains weight, is the most-consistent known environmental risk for breast cancer, according to the review of available data by the Institute of Medicine, a nonprofit group that advises the government on health issues.
The lack of clear ties between chemicals and other possibly toxic substances and breast cancer doesn’t mean they are safe, said Irva Hertz-Picciotto, chair of the IOM committee and chief of environmental and occupational health at the University of California, Davis’ School of Medicine.
“In many cases, it’s because good human studies haven’t been conducted yet, not because they have been conducted and rejected the hypothesis,” she said in an interview. “That is the critical piece here. We think there could be exposures very early in life that influence the risk of cancer decades later.”
More work is needed to move suspected dangers to the “probable” list of cancer-causing agents, said David Hunter, a professor of cancer prevention at Harvard School of Public Health in Boston, and a study author. The review, presented at the San Antonio Breast Cancer Symposium, identified hormone therapy like Pfizer Inc.’s Prempro, weight gain after menopause, and radiation from medical tests like CT scans as triggers. Early research when girls’ breasts are growing is key, he said.
“We need to focus on a woman’s whole life course, not just a few years prior to a breast cancer diagnosis,” Hunter said. “What happens during childhood, and even in utero, may be important.”
The institute study ruled out risk from hair dyes and radiation found in devices like mobile phones and microwaves.
While chemicals including those in gas fumes and car exhaust such as benzene may trigger tumors, others including BPA and pesticides have less evidence implicating them, Hunter said. It’s hard to get conclusive results because chemicals are so prevalent, and may be most harmful earlier in life, he said.
The 350-page report, commissioned by Susan G. Komen for the Cure, took at broad look at the environmental causes of breast cancer. More than a dozen academic leaders in oncology, environmental and occupational health examined research on every aspect of life that occurs outside the genes women inherit from their parents to pinpoint potential dangers.
Damage to Cells
Breast cancer is the most-common tumor type outside of skin cancer in women, with an estimated 230,480 new cases this year. Almost 40,000 women die each year in the U.S. from breast cancer, making it the second-deadliest tumor after lung cancer. It is believed to stem from accumulated damage to the cells from genetics and external factors, according to the report.
One of the most-important conclusions is that women should work with doctors to understand their individual risk, said Kathy Helzlsouer, director of the prevention and research center at Johns Hopkins University in Baltimore.
While steps can be taken to minimize the chances of developing breast cancer, only women at high risk may want to use more-aggressive measures, she said.
The generic drug tamoxifen and Eli Lilly & Co.’s Evista are good options to prevent tumors in high-risk women, Helzlsouer said in a telephone interview. Medical imaging with x-rays and CT scans are sometimes necessary, though excessive testing should be avoided, she said.
A glass of wine or a similar daily drink also raises breast cancer risk by about 9 percent, Hunter said. On the other hand, alcohol lowers heart disease risk, again pointing to the need for individual lifestyle decisions, he said.
“Breast cancer develops over many years, so we need better ways to study exposures throughout women’s lives, including when they are very young,” Hertz-Picciotto said. “We also need improved methods to test for agents that may be contributing to breast cancer risk.”