Breast density risk for cancer
Numerous studies have shown that the density of breast tissue is related to breast cancer risk. Women who have breasts with dense tissue are 4 to 6 times more likely to develop breast cancer than those who have little tissue density.
But until recently it was thought that the link between breast density and breast cancer might be related to how breast density impacts on discovering the cancer itself – in other words, the breast tissue would mask a tumour on a mammogram.
But a recent Canadian study has shown that the connection may be much more direct. Scientists at The Campbell Family Institute for Breast Cancer Research at Princess Margaret Hospital compared different breast densities with the risk of breast cancer in more than 1,000 women with breast cancer and 1,000 who did not have the disease. The women were screened in the National Breast Screening Study, The Ontario Breast Screening Program and the Screening Mammography Program of British Columbia.
The study found that the risk of breast cancer was about five times greater in women with extensive dense tissue in the breast compared to those with little or no dense tissue.
“Depending on a woman’s age, between 16-30 per cent of breast cancers can be attributed to extensive density,” says Dr. Norman Boyd, a principal investigator in The Campbell Family Institute for Breast Cancer Research at Princess Margaret Hospital and a professor at the University of Toronto, in a January 2007 press release. “Other risk factors, including family history and the known genes, account for a much smaller proportion of the disease.”
This may seem like good news for those who worry about breast cancer because it has run in their family. But the bad news is that breast density also has a genetic component, so it may still be an inherited trait.
Breast tissue is mainly made up of two forms of tissue: ductal tissue and fatty tissue. A breast is said to be dense if it is more ductal tissue than fatty tissue. Breast size is not necessarily a good way to measure breast density, although it may be in women who are very lean: thin women with larger breasts may have more ductal tissue than average. Breast implants have not been shown to impact on the risk of breast cancer.
Breast cancer is the most frequently diagnosed cancer in women in Canada. According to the Canadian Cancer Society, on average, 429 Canadian women will be diagnosed with breast cancer every week and 102 Canadian women will die of breast cancer every week.
Other risk factors include (from Health Canada):
• Being overweight/obese (only after menopause), based on your BMI
• Taking hormone replacement therapy
• Exposure of the breast to high levels of ionization radiation (i.e. x-rays) or lower levels before age 2, especially at a young age
• Having a first baby after age 30 or never having a baby
• Never breastfeeding
• Having a close relative(s) with breast cancer
• Gender: More than 99 per cent of breast cancers occur in women
• Age: risk increases as you get older
• Early menstruation (before the age of 12)
• Late menopause (after age 55)
If you are a woman between 50 and 69 years of age, Health Canada recommends that you have a screening mammogram (a breast cancer screening x-ray) at least once every two years based on your personal risk factors and the advice of your health care provider. Dense breasts can make screening more difficult; it’s harder to find a small tumour, so additional screening may be advised.