Girls born to mothers over 39 years and women who were taller and thinner than the average girl prior to puberty faced higher chances of developing breast cancer.
These findings were based on an analysis of a sample of 3,574 women aged between 45 and 68 years, assisted by the screening programmes of seven of Spain's autonomous communities.
Although the role of breast density in breast cancer has been known, researchers at the Carlos III Health Institute (ISCIII), Spain, have now explored the influence of certain characteristics on breast density, the journal Breast Cancer Research and Treatment reports.
Breast density refers to women who have more fibrous connective and glandular tissue than fatty tissue. It can make breast cancer difficult for a radiologist to see on a mammogram, according to an ISCIII statement.
Virginia Lope, researcher at the National Centre for Epidemiology at the ISCIII, explains that "accumulated exposure to hormones along with growth factors in the earlier stages of life when the breasts begin to develop both condition breast tissue composition and influence the probability of developing a tumour as an adult".
During the 2010 annual meeting of the American Association for Cancer Research (AACR), various studies were presented that showed that women with a mammographic density of 75 percent or above are five times more likely to develop breast cancer in comparison to women with a low density.
Furthermore, studies demonstrate that women who experience a reduction in breast density over six years are less at risk than those whose breast density remains stable.
Although breast density is clearly hereditary, other factors have an influence. These include the age of the woman when she has her first child and the number of children she has.
The authors conclude that "many studies used mammographic density to investigate the possible influence of other exposures in breast cancer risk".