Does dense breast tissue increase cancer risk?

When a woman gets a mammogram, her doctor examines the x-ray pictures to see if the breast tissue displays characteristics that could indicate the presence of cancer. One of the dilemmas in interpreting mammograms is the presence of tissue that may mimic cancer, a common finding, especially in premenopausal women. In most women, the breasts are made mostly of fat, which appears black on a mammogram. Some women have what is known as "dense" breast tissue, which means it contains less fat than usual and more fibrous tissue or tissue consisting of breast or mammary glands. This dense tissue appears white on a mammogram. 

The difficulty arises in interpreting the cause of white tissue on a mammogram because while normal dense tissue appears white, so does cancer. If the white area appears in the background of surrounding fatty tissue, the possibility that it is more likely to be cancer. If a possible tumor is surrounded by dense, fibrous tissue, the person interpreting the mammogram cannot distinguish the actual composition of that white area, which may contain cancer or normal dense tissue. In cases like this, an ultrasound is often recommended. Experienced mammographers can then better determine whether the white tissue is benign or cancerous. However, the only way to be absolutely sure about the tissue composition (whether it is cancer or benign) is to have a biopsy.

What's New

A study recently published in the New England Journal of Medicine found that not only was breast cancer harder to detect in women with dense breast tissue, but these women were also more likely to get breast cancer. If you have dense breasts (ask your doctor if you're not sure), don't panic—having dense breasts certainly doesn't mean that you definitely will develop breast cancer—in fact, most of the estimated 10% of women with highly dense breasts will never develop breast cancer. And about 75% of women with breast cancer do not have highly dense breasts.

Though it is one of the more powerful risk factors, breast density is just one factor that increases the risk of breast cancer. Others include:

• A family history of the disease
• Mutations in certain genes
• Beginning menstruation at an early age (before age 12) or going through menopause at a late age (after age 55) have a slightly higher risk of breast cancer.
• Long-term use of hormone replacement therapy
• Being older that 30 when you first get pregnant
• Never carrying a pregnancy to full term
• Never breastfeeding a baby

And whether you have dense breast tissue or not, all women should take steps to reduce their risks of breast cancer, including:  

• Keeping at a healthy weight, especially after menopause
• Drinking alcohol in moderation, if at all. 
• Not smoking
• Keeping physically active 

Scientists have also been actively engaged in research to see whether lowering the levels of estrogen in a woman can make it easier to detect cancer. This lowering of estrogens, which is induced by specialized medicines, has undergone study in Europe, with some promising results. Additional research is likely to help physicians detect irregularities in the breast more easily and therefore need to rely on biopsy less often. 

Have you ever been told you have dense breasts? Have you needed to get further testing after a clinician spotted white tissue on a mammogram?

Marc Garnick, M.D., is an internationally renowned expert in medical oncology and urologic cancer, with a special emphasis on prostate cancer. He is a Clinical Professor of Medicine at Harvard Medical School and maintains an active oncology practice at Beth Israel Deaconess Medical Center. Dr. Garnick serves as Editor in Chief of Perspectives on Prostate Diseases, a quarterly report from Harvard Health Publications.

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