Breast cancer prediction and prevention could start younger

Medical Tribune July 2009 P13
David Brill

Risk assessment for breast cancer could one day start in girls as young as 15, according to a recent paper which may open up new opportunities for early disease prevention.

Canadian researchers found that breast tissue composition – a known risk factor in middle age and above – begins to vary at a much younger age, and could provide a quantifiable way to predict risk.

It is the first extensive study to look at breast tissue composition in young women, say the authors, who used MRI in order to avoid the radiation exposure of mammography.

Percent breast water was found to decrease with age (P=0.04) – a finding which could explain why breast tissue is thought to be most susceptible to carcinogens at a young age.

The researchers also found strong correlations to height and weight – suggesting that breast composition could be influenced by factors relating to growth and development. Percent breast water was also strongly linked to mammographic density in the subjects’ mothers – lending support to a hereditary component to breast formation.

“What [this study] suggests is that prevention is going to be most effective if started earlier in life, and that measurement of breast tissue characteristics might be one way of modifying and monitoring prevention,” said lead author Professor Norman Boyd, of the Campbell Family institute for Breast Cancer Research, Toronto, Canada.

Further research is needed before risk assessment could be practiced routinely in young girls, said Boyd, noting two key areas of uncertainty. First would be to establish the most appropriate method for assessing breast composition in young women, and second would be to be determine which interventions would be appropriate and safe in those found to be at high risk.

“The long-term vision would be that we would have a method of assessing breast tissue composition as soon as the breast forms, essentially. MRI is what we’ve used, but MRI is clearly not the answer to this because it’s so expensive and there are so few machines,” he said.

“It’s difficult to know how technology is going to advance but at the moment, ultrasound looks very appealing. It can be done quickly, it can be done quantitatively, it can give us measurements of tissue volumes, which mammography does not do, it can be done very, very quickly… and it’s completely free of risk.”

Boyd and colleagues measured levels of water and fat in the breasts of 400 women aged 15 to 30, and their mothers. The percentage of water on MRI correlated strongly with mammographic density in a randomly selected subset of 100 of the mothers (r=0.85). [Lancet Oncol 2009 Apr 29; Epub ahead of print]

Height, weight and maternal mammographic density were all strongly associated with per cent breast water in young women (P<0.0001). Height and weight also correlated strongly to total breast fat, and maternal mammographic density correlated strongly to total breast water (P<0.0001).

The association between weight and percent breast water was inverse – suggesting that heavier young women are at lower risk of breast cancer. Previous studies have also shown similar findings but the mechanisms for the association remain unclear, said Boyd. The authors did, however, report an association between percent breast water and serum levels of growth hormone – a finding which could underlie the associations with height and weight, they say.

Further research is already ongoing to better understand the genetic factors that influence breast composition, added Boyd.