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Girls at risk. Although the associations between smoking and breast cancer are complex, a study by researchers at the School of Public Health concludes that young girls exposed to secondhand smoke are at increased risk of breast cancer later in life.

SPH research associate Timothy Lash and Associate Professor Ann Aschengrau studied women in Massachusetts over a three-year period, comparing those who were exposed to smoke -- both by smoking and by being passively exposed -- and paying particular attention to the stage of development when exposure began.

The results are contained in a chapter in the forthcoming book Environmental Tobacco Smoke, edited by Ronald R. Watson and Mark Witten. Lash, Aschengrau, and coauthor Alfredo Morabia, explain that breast cells change throughout a woman's lifetime, transforming at reproductive milestones -- sexual maturity, pregnancy, lactation -- and reverting to earlier forms after lactation and during menopause. The cells are most susceptible to carcinogens before sexual maturity, while they are still developing. This has also been observed in studies of female survivors of the atomic bomb. Those exposed to radiation before age 9 had the highest relative risk of later developing breast cancer, followed by women between the ages of 10 and 19.

If, as many scientists believe, the development of breast cancer is a two-stage process -- involving an initial mutation in the breast tissue cells that may later be triggered by a second event producing cancer -- the effects of a carcinogen such as environmental smoke may have no obvious effect until many years later.

Further study is needed, say the researchers, to better understand how other factors, such as heredity and the tendency of tobacco smoke to depress estrogen levels, interact with tobacco smoke exposure at different developmental stages. They hope that the studies will produce recommendations for lifestyle changes that can reduce the risk of breast cancer for women at all ages.

Brighter is not always better. Contrary to generally accepted theories of sexual selection, bright plumage may not be an advantage for young male lazuli buntings, a socially monogamous songbird found throughout the western United States and Canada.

According to a recent study by Steven Oliver, a graduate student at the Boston University Marine Program, in Woods Hole, Mass., and colleagues at the Universities of Montana and California--Santa Cruz, and Queen's University in Ontario, the most successful yearlings -- those that were able to claim nesting territory, mate, and sire young -- were either among the dullest or the brightest in the vicinity, but not those in the middle.

Adult male lazuli buntings have brightly colored turquoise heads and rusty-orange breasts. The plumage of young birds, or yearlings, however, can vary greatly, from the dull brown of the females to the bright colors of the adult male. In the spring, the older males return to the breeding grounds first, claiming the best, most protected nesting territory and vigorously defending their claim against newcomers.

The researchers observed that although adult males react aggressively toward the brighter males, they tolerate the dull yearlings, allowing them to settle nearby in high-quality habitats. The brightest yearlings were also successful, since they were generally aggressive enough to compete with the adults for nesting sites. The researchers speculate that the less attractive dull males do not pose as much of a threat to the adult birds, and that in fact, both the adults and dull yearlings benefit from this arrangement.

The dullest males do, however, pay a price for this success. Their partners often also mate with their older, bright neighbors. The dull males raise some chicks of their own, at the cost of also raising some offspring of the older birds. This is better than the situation of the intermediate males, who often raise no offspring in their first year. The dull males, the study says, make "the best of a bad situation," and illustrate "a rare example of sexually selected male-male cooperation."

The study was published in the October 26 issue of the journal Nature.

"Research Briefs" is written byJoan Schwartz in the Office of Provost. To read more about BU research, visit http://www.bu.edu/research.

10 November 2000
Boston University
Office of University Relations