Risk Factors for Breast Cancer

The Breast Density — Breast Cancer Connection

Researchers at Harvard Medical School and Brigham and Women’s Hospital in Boston have recently published a new study that indicates that postmenopausal women whose breasts appear dense on mammograms have a higher risk for some aggressive breast cancers. High breast density is described as having relatively little fat in the breast and more connective and glandular tissue. A woman’s breast density is pretty much the result of  genetic endowment. The good news for postmenopausal women is that as we get older out breast become fattier and less dense.

The Harvard study compared the breast density in 1,042 postmenopausal women who had breast cancer and 1,794 age-matced women who did not havr breast cancer. All were participants in the Nurse’s Health Study, which has followed more than 120,000 women for 35-years. Women with 50% or higher breast density on a mommagram were three times more likely to be diagnosed with breast cancer over a 15-year period than women with less then 10% breast density. The link was stronger for in situ tumors (cancer confirned to the ducts or lobules) than for invasive tumores, but it was also stronger for more aggressive breast cancers — including larger tumors (which are more likely to grow and spread than low grade tumors0, and estrogen receptor (ER)-negative tumors, which tend to recur faster and can be more difficult to treat than ER-positive tumors.

The findings appeared online July, 27, 2011, and in print, August 3, 2011 in the Journal of Nation Cancer Institute.

If you are post menopausal and have dense breast here are some points to ponder.

  • Mammograms are less sensitive for women with dense breast tissue than women with fattier breast, so you will likely be called back for additional images or even a biopsy.
  • Hormone therapy increases breast density, so if you are considering HRT for severe menopausal symptoms, you may wish to explore other options.
  • If your overall risk of breast cancer is high, you may want to consider chemoprevention with tamoxifen, which can reduce breast density. A 2008 study showed that women whose breast density decreased by 10% or more within the first year or so on tamoxifen were 63% less likely to develop breast cancer than women taking a placebo.
  • Mammography has been the main focus of breast cancer detection, but almost half of breast cancers in women ages 50 to 69 are first found by the women themselves or their clinicians, according to a study in August 2011 Journal of Woman’s Health. So the best advice of all is to be familiar with the architecture of your breasts, and let your doctor know immediately if you note any changes.
  • Breast density is an important risk factor but not the only one. See list below:

Not all women have the same risk for developing breast cancer over a lifetime.

Certain factors increase a woman’s risk, and some have a bigger impact on risk than others. However, having several risk factors doesn’t mean you’ll inevitably develop breast cancer. Likewise, having few risk factors doesn’t mean that you’ll never develop it.

Many risk factors, such as age and gender, are not within our control. Others, especially those related to personal behaviors, can be modified.

It’s important to know about risk factors because they can help identify women who might benefit from certain preventive strategies. A woman should work with her clinician to determine her personal risk for breast cancer and plan screenings, office visits, and preventive care accordingly. Online resources that can help in determining risk include the Breast Cancer Risk Assessment Tool (www.cancer.gov/bcrisktool) and Harvard School of Public Health’s “Disease Risk Index” (www.diseaseriskindex.harvard.edu).

Known risk factors for breast cancer include the following:

Gender. This is the strongest risk factor for breast cancer. Men can develop breast cancer, but it’s 100 times more common in women than men, mostly because women’s breast tissue is far more exposed to hormones such as estrogen that promote abnormal cell growth.

Age. This is one of the strongest risk factors for breast cancer. About 85% of cases occur in women ages 50 and over, while 5% occur in women under age 40.

Family history. Women who have two or more first-degree relatives (mother, daughter, sister) with breast or ovarian cancer have a greater than 50% chance of developing breast cancer. One of the main reasons for this elevated risk is an inherited mutation in one of two genes, BRCA1 and BRCA2. Other gene mutations can also lead to inherited breast cancer, but these are rarer and don’t affect risk as much BRCA mutations. Inherited risk accounts for 5% to 10% of breast cancers.

Previous breast cancer. If you’ve had cancer in one breast, you have a three- to four-fold increased risk of developing a new cancer in the other breast or another part of the same breast. (This is not the same as a recurrence of the original cancer.)

Breast density. Women with denser breast tissue, as seen on a mammogram, have a higher risk for breast cancer than women whose breasts are relatively more fatty. The greater the proportion of dense breast tissue on a mammogram, the higher the risk.

Certain benign breast conditions. Women who’ve had biopsies that show an overgrowth of cells (hyperplasia) in the ducts or lobules have an increased risk for breast cancer, particularly if the cells appear abnormal (a condition called atypical hyperplasia). Benign breast conditions that don’t cause this type of overgrowth do not appear to increase risk; these include fibrocystic disease, simple fibroadenoma, mastitis, fat necrosis, and benign tumors.

Lobular carcinoma in situ (LCIS). Women with LCIS are at increased risk of developing breast cancer in either breast.

Exposure to radiation. Women who’ve had high-dose radiation to the chest as part of treatment for another cancer (such as Hodgkin’s disease) have an increased risk of developing breast cancer, especially if they underwent radiation during adolescence. Radiation after age 40 does not appear to increase breast cancer risk.

Race. White women are slightly more likely to develop breast cancer than African-American women, but African-American women are more likely to die of the disease. Asian, Hispanic, and Native American women appear to have a lower risk than white or African-American women of developing and dying from breast cancer.

Estrogen exposure. The longer a woman is exposed to estrogen, the greater her risk for breast cancer. Multiple pregnancies and pregnancy at a young age reduces a woman’s total number of menstrual cycles and thus her risk of breast cancer, though this is not as strong a risk factor as many others. Women who menstruate early, before age 12, and/or go through menopause late (after age 55) have a slightly higher risk of breast cancer, possibly because of the increased lifetime exposure to estrogen. Current oral contraceptive use slightly increases breast cancer risk, but it returns to normal once the pills are stopped. Current or recent use of postmenopausal hormone therapy with estrogen plus a progestin increases breast cancer risk within as few as two years; risk returns to normal within five years of stopping. (Postmenopausal hormone therapy with estrogen alone does not appear to increase breast cancer risk.)

Diethylstilbestrol (DES) exposure. Women who took DES — a drug used from the 1940s through the 1960s to prevent miscarriage and since banned — have a slightly higher risk of developing breast cancer. Their daughters may also.

Weight. Being overweight or obese has been linked to breast cancer risk, especially for women after menopause, but the relationship is complicated. It may be that risk is increased in women who gain weight in adulthood but not in those who’ve been overweight since childhood.

Alcohol. Women who drink alcohol have an increased risk of breast cancer, compared with women who don’t drink, and the risk rises with the number of drinks consumed.

Other cancers. Women who’ve been diagnosed with cancer of the ovary, colon, or endometrium are more likely to develop breast cancer than women who don’t have these cancers.


Harvard Women’s Health Watch; Volume 19.Number 2.October 2011

Journal of Nation Cancer Institute, August 3, 2011

Journal of Woman’s Health, August 2011


Author: H. Sandra Chevalier-Batik

I started the Inconvenient Woman Blog in 2007, and am the product of a long line of inconvenient women. The matriarchal line is French-Canadian, Roman Catholic, with a very feisty Irish great-grandmother thrown in for sheer bloody mindedness. I am a research analyst and author who has made her living studying technical data, and developing articles, training materials, books and web content. Tracking through statistical data, and oblique cross-references to find the relevant connections that identifies a problem, or explains a path of action, is my passion. I love clearly delineating the magic questions of knowledge: Who, What, Why, When, Where and for How Much, Paid to Whom. My life lessons: listen carefully, question with boldness, and personally verify the answers. I look at America through the appreciative eyes of an immigrant, and an amateur historian; the popular and political culture is a ceaseless fascination. I have no impressive initials after my name. I’m merely an observer and a chronicler, an inconvenient woman who asks questions, and sometimes encourages others to look at things differently.