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.
NEW YORK--The timing of exposure to environmental factors may be themost powerful determinant in the development of breast cancer, Mary Wolff,PhD, said in a lecture sponsored by the Irvington Institute for ImmunologicalResearch.
Evidence from epidemiologic and laboratory studies, in both humans andanimal models, suggests that puberty represents a particularly vulnerabletime in terms of breast cancer induction, said Dr. Wolff, professor ofcommunity 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, areat increased risk, since their exposure to estrogen is over a longer periodof time.
A worldwide decline in the average age at menarche, from 17 years in1800 to 13 years today, and as young as 12 years in developed countries,parallels a rise in breast cancer incidence. Dr. Wolff said that becausepuberty is a time of rapid cell division and development, it makes sensethat breast and other cells are more susceptible to environmental insultsduring that period.
A comparison of breast cancer in white and African-American women implicatesdifferences in estrogen exposure, she said. Although the breast cancerincidence is similar between white and African-American women, the agecurve differs. "Up to age 40, black women are at higher risk thanwhite women," she said. "But as they get older, their risk islower."
This has clinical significance because younger women tend to have poorerprognoses, possibly because more aggressive tumors tend to develop in womenwith more active hormones.
The explanation might lie in the fact that in the United States, African-Americanwomen have earlier menarche but also earlier menopause, she said.
Studies have shown that African-American girls are three times morelikely than white girls to show signs of puberty (breast development andthe appearance of pubic hair) at age 6.5 years (48% versus 15%). By age9.5 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 riskfor breast cancer by 10% to 20%," Dr. Wolff said. "In the UnitedStates, that would represent as many as 15,000 to 35,000 fewer cases peryear."
Lifestyle changes that may help reduce cancer risk should be encouragedin children, Dr. Wolff said. Strenuous exercise around puberty may be protective,she said. A low-fat diet including ample fruits and vegetables, as in theFDA's "Food Pyramid" is important. But Dr. Wolff pointed to arecent survey showing that preadolescents rarely comply with the Food Pyramidrecommendations.
She also noted that phytoestrogens (found principally in soybeans andother soy products) and dietary fiber are thought to be particularly protective.
"Considering the vulnerability on a cellular level during the yearssurrounding puberty, these preventive strategies are well worth applyingin the young," Dr. Wolff said.