NEW YORK--The timing of exposure to environmental factors may be the most powerful determinant in the development of breast cancer, Mary Wolff, PhD, said in a lecture sponsored by the Irvington Institute for Immunological Research.
Evidence from epidemiologic and laboratory studies, in both humans and animal models, suggests that puberty represents a particularly vulnerable time in terms of breast cancer induction, said Dr. Wolff, professor of community medicine, Mt. Sinai School of Medicine, NY.
An important and potentially modifiable risk factor is exposure to estrogen, she said. Women who have early menarche or late menopause, or both, are at increased risk, since their exposure to estrogen is over a longer period of time.
A worldwide decline in the average age at menarche, from 17 years in 1800 to 13 years today, and as young as 12 years in developed countries, parallels a rise in breast cancer incidence. Dr. Wolff said that because puberty is a time of rapid cell division and development, it makes sense that breast and other cells are more susceptible to environmental insults during that period.
A comparison of breast cancer in white and African-American women implicates differences in estrogen exposure, she said. Although the breast cancer incidence is similar between white and African-American women, the age curve differs. "Up to age 40, black women are at higher risk than white women," she said. "But as they get older, their risk is lower."
This has clinical significance because younger women tend to have poorer prognoses, possibly because more aggressive tumors tend to develop in women with more active hormones.
The explanation might lie in the fact that in the United States, African-American women have earlier menarche but also earlier menopause, she said.
Studies have shown that African-American girls are three times more likely than white girls to show signs of puberty (breast development and the appearance of pubic hair) at age 6.5 years (48% versus 15%). By age 9.5 years, the difference is 77% for African-American girls versus 38% for white girls.
"As little as a one-year delay of menarche might reduce the risk for breast cancer by 10% to 20%," Dr. Wolff said. "In the United States, that would represent as many as 15,000 to 35,000 fewer cases per year."
Lifestyle changes that may help reduce cancer risk should be encouraged in children, Dr. Wolff said. Strenuous exercise around puberty may be protective, she said. A low-fat diet including ample fruits and vegetables, as in the FDA's "Food Pyramid" is important. But Dr. Wolff pointed to a recent survey showing that preadolescents rarely comply with the Food Pyramid recommendations.
She also noted that phytoestrogens (found principally in soybeans and other soy products) and dietary fiber are thought to be particularly protective.
"Considering the vulnerability on a cellular level during the years surrounding puberty, these preventive strategies are well worth applying in the young," Dr. Wolff said.