A new study has reported that women with a family history of breast cancer tend to have dense breasts and that this partially explains their increased risk of breast cancer. Breast density, as measured by mammography, has been found to be a strong and highly heritable breast cancer risk factor. The authors performed three nested case-control studies in screening programs that included a total of 2,322 participants (1,164 breast cancer cases and 1,158 cancer-free controls). Family history was defined for purposes of the study as having at least one first degree relative (parent, sibling or child) with breast cancer. The analyses were performed while adjusting for age and other breast cancer risk factors.

Compared to women without any first-degree relatives with breast cancer, percent mammographic density was found to be 3.1% higher in women with such relative, and 7.0% higher in women with two or more such affected relatives. The risk of breast cancer was 37 percent higher among women having one first degree relative with breast cancer than among those without any such relatives. Women with two or more affected first degree relatives had almost two and one-half times the risk of breast cancer. Adjusting for percent mammographic density reduced these odds; mammographic density was found to explain 14% of the association between having at least one affected first-degree relative and risk of breast cancer. The authors conclude that some of the genes that explain variation in breast density might also be associated with familial cancer risk.

If you have a family history but have not been diagnosed with breast cancer

This study confirms the findings of previous studies that have reported a strong association between dense breasts and heightened risk of breast cancer. For women with a family history of breast cancer, the question is what to do with this information. We suggest the following:

  • Women with at least one first degree relative with breast cancer should start getting mammograms and other types of breast cancer screening at a younger age than the general population (by age 30 or the age recommended by your cancer specialist). One recent study found that women with a family history had a greater risk of breast cancer at an earlier age, especially when the older relative was diagnosed at a relatively young age. For example, daughters of mothers who were diagnosed with breast cancer before age 40 were found to reach the level of risk that women lacking a family history had at the age of 50 approximately 12.3 years earlier
  • This brings up our second suggestion, which is to join a respected cancer center program for high-risk women ahead of any breast cancer diagnosis. This will provide you with cancer specialists who can advise you on when to get mammograms and other forms of breast cancer screening, among other benefits
  • Make sure that your mammographic density is evaluated and taken into account when planning your screenings. Mammograms of dense breasts can be difficult to read. Breast sonograms sound low tech, but they can effective in evaluating a possible mass in mammographically dense breasts, as long as the staff is competent in performing such readings
  • Adopt a diet emphasizing foods containing carotenoids (e.g., bell peppers, carrots, kale, oranges, pumpkins, tomatoes, watermelon, and zucchini) and vitamin D from our recommended food list and avoid the foods on our avoid list, especially animal proteins such as beef, cheese, milk, pork, lamb and processed meats.

Similar advice with respect to diet applies to breast cancer survivors with dense breasts. Such women should also be aware that they have a higher than average risk of local recurrence (in the same or opposite breast) and that radiation treatment has been found to be important in reducing such risk.