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By Denise Mann
THURSDAY, April 30, 2009 (Health.com) — Young women with dense breasts—as measured by the percentage of water in their breast tissue—may be at greater risk of developing breast cancer later in life than women with less-dense breasts.
According to a report in Lancet Oncology, breast cancer screening, which women typically start in their 40s and 50s, may be useful when started earlier in life. "The findings may lead us toward characterizing risk earlier then we do now and intervening to prevent breast cancer earlier than we do now," says lead researcher Norman Boyd, MD, a scientist at the Campbell Family Institute for Breast Cancer Research at Princess Margaret Hospital in Toronto.
In the study, the researchers used MRIs to examine the breast tissue of 400 mother-daughter pairs, including younger women aged 15 to 30. All of the mothers also had mammograms.
The researchers found that the daughters' breast density as measured by MRI was associated with their mothers' breast density as measured by mammogram. The researchers also found that the younger the girls were, the greater the breast density and the percentage of water in breast tissue. For example, girls aged 15 to 19 had higher percentages of water in their breast tissue than those aged 20 to 30.
What's more, the water percentage increased with height. Specifically, for each 5-centimeter difference in height among the daughters, there was a 3% increase in the percentage of water in breast tissue. Some previous studies have suggested that taller women are more likely to develop breast cancer than shorter women.
The link may be due to growth hormone—girls with higher levels of growth hormone are taller and have denser breasts.
Would blocking growth hormone help prevent or treat cancer? "There is evidence from animals and rats that blocking growth hormone may prevent cancer, but there is no direct evidence from humans yet," Dr. Boyd says. That said, it is possible that measuring growth hormone in the blood of women may help predict future risk of breast cancer, he says.
"We have known for a while that breast density in adult women correlates with higher risk of breast cancer," explains Marisa Weiss, MD, president and founder of the advocacy group breastcancer.org and the author of several books, including Taking Care of Your Girls: A Breast Health Guide for Girls, Teens, and In-Betweens. "The younger you are, the more dense the breast tissue is and the taller you are, the denser it is. But what we don't know is if breast density changes," says Dr. Weiss, who is the director of breast radiation oncology and breast health outreach at Lankenau Hospital in Wynnewood, Penn.
"The study captures just one moment in time," she says. "We need more studies to understand what breast density means in girls and whether it changes as they grow."