Humans put a lot of stock in symmetry. People with symmetrical faces, for example, are often viewed as more attractive and mate-worthy. But the advantages don't end there. According to a new study, women with more symmetrical breasts have a lower chance of developing breast cancer than those with less mirror-perfect breasts.
Many factors are known to influence the risk of breast cancer: inherited gene mutations (ScienceNOW, 26 November 26 2003), duration of breast feeding (ScienceNOW, 18 July 2003), and exposure to second-hand cigarette smoke (ScienceNOW, 11 April 2000), for example. Another difference between healthy women and those with breast cancer is that the latter group has more asymmetrical breasts. The question was: Could breast asymmetry predict breast cancer risk when measured in healthy women?
Preliminary findings suggest it might. In a study published today in Breast Cancer Research, medical imager Diane Scutt and Gillian Lancaster from the University of Liverpool, U.K., and John Manning from the University of Central Lancashire, U.K., measured breast volume from the mammograms of 504 healthy women. Breast asymmetry was fairly common. Among women who stayed healthy, one breast was on average 53 milliliters, or 2.5%, bigger than the other; for those who developed cancer, the difference was significantly higher: 63 ml or 2.7%. The researchers calculated that, for every 100-milliliter difference in breast volume, there was a 50% increase in risk.
Such an extreme volume difference is found in very few women, says Scutt, who notes that other factors must be taken into account when assessing cancer risk. Still, she says, doctors may ultimately be able to use measurements of breast asymmetry to monitor women already at high risk for breast cancer.
Anthropologist Robert Trivers, of Rutgers University in New Brunswick, New Jersey, who studies the effects of asymmetry, agrees and says the findings make sense; breast asymmetry is caused by fluctuating estrogen levels, which are also associated with other breast cancer risk factors. He adds that the study is potentially "valuable" for quantifying the risk from asymmetry.