You may not have given much thought to the density of your breasts. But dense tissue makes tumors hard to detect, and it's more susceptible to tumor growth. In the most comprehensive study on density yet, researchers have found exactly how risky this tissue can be.
For the most part, density is inherited, and it declines with age. Having children later in life—or not at all—will preserve density, and hormone replacement therapy will increase it. You can find out how dense your breasts are with a mammogram. Radiologists generally score breasts in one of four categories that roughly correlate to Boyd's classifications: fatty (less than 25 percent dense tissue), scattered (25 to 49 percent), heterogeneous (50 to 74 percent), or extremely dense (more than 75 percent). "We eyeball it," says Roxanne Lorans, MD, a radiologist at the Mayo Clinic in Arizona. "But we're pretty close to the mark."
While every mammogram report includes a density score, few doctors share it with their patients, says Karla Kerlikowske, MD, professor of medicine, epidemiology, and biostatistics at the University of California, San Francisco. "At this point, we're still educating physicians." In the meantime, patients should ask for their score.
Protecting yourself: Women worried about their breast density should consider getting digital mammograms, says Susan Love, MD, president and medical director of the Dr. Susan Love Research Foundation. With a standard mammogram, dense tissue appears light, the same as tumors, so it can mask the cancer. "It's like trying to find a polar bear in the snow," says Love. According to results reported in 2005 from the Digital Mammographic Imaging Screening Trial, digital mammograms are better than film-screen mammograms at detecting tumors in dense breasts.
Also be diligent about monthly breast self-exams. You can decrease your risk of breast cancer in general by exercising, limiting alcohol, and watching your weight.
One thing to avoid is panic. The average 50-year-old woman has about a 2.5 percent chance of getting breast cancer in the next ten years. If she has density in more than half the breast, the number climbs to about 5 percent. "Even though density is a strong risk factor," says Boyd, "the majority of women with high levels will not get the disease."