Q:

I've heard that women with denser breast tissue have a higher risk of certain breast cancers. I am a 63-year-old, postmenopausal woman, and my doctor has told me that I have very dense breasts. I get regular mammograms, but I'm still worried that I have a high risk for cancer. Should I be worried?

A:

It's true that one of the strongest known risk factors for breast cancer is high breast density. The reason for this is poorly understood, but we'll walk you through the current thinking on the matter.

First, let's talk about what tissue density means when it comes to the breasts. A woman with dense breast tissue has relatively little fat in the breast and more connective and glandular tissue, as seen on a mammogram.

Research has indeed found that higher breast density in postmenopausal women increases the risk of specific types of breast cancer. This includes some types that have a relatively poor outlook.

In one study, women with 50 percent or higher breast density on a mammogram were three times more likely to be diagnosed with breast cancer over a 15-year period than women with less than 10 percent breast density.

The link between breast density and breast cancer was stronger for cancer confined to the ducts or lobules of the breast than for invasive tumors. It was also stronger for more aggressive breast cancers. These include larger tumors, high-grade tumors, which are more likely to grow and spread than low-grade tumors, and estrogen receptor (ER)ñnegative tumors. The latter tend to recur sooner and be more difficult to treat than ER-positive tumors.

Researchers have suggested that the link between breast density and more aggressive tumors may have something to do with the fact that it's harder to spot cancers in dense breasts on a mammogram. In other words, denser breast tissue may mask or hide aggressive tumors until they're larger and more dangerous.

However, other studies have shown that the link between breast density and breast cancer risk is strong even without taking this masking effect into account.

Like your gender, your race, your family history and your genes, breast density is pretty much out of your control. The good news is that as women age, their breasts tend to become fattier and less dense. Still, some women like you continue to have dense breast tissue well into their postmenopausal years.

In cases like yours, mammograms are less sensitive than they are for women with fattier breasts. This means you're more likely to be called back for additional images or to undergo a breast biopsy. Your radiologist may also want to take more images using a different method.

Hormone therapy increases breast density, so if you're considering it for severe menopausal symptoms, you may want to explore other options.

If your overall risk for breast cancer is high, you may want to ask your doctor about prevention with tamoxifen, an estrogen-blocking drug that can reduce breast density and lower the risk of breast cancer. A 2008 study showed that women whose breast density decreased by 10 percent or more within the first year or so on tamoxifen were 63 percent less likely to develop breast cancer than women taking a placebo. Unfortunately, though, tamoxifen has side effects, some of which can be serious.

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. So be familiar with the architecture of your breasts, and bring any worrisome changes to your doctor's attention as soon as possible.

Breast density is an important risk factor for breast cancer, but it's not the only one. You and your doctor should know your risk profile and plan screenings and office visits accordingly. And, unlike breast density, there are factors within your control that can help reduce your breast cancer risk.

First, keep your weight under control and within a healthy range. 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.

Controlling your alcohol intake can also help. Women who use alcohol have an increased risk of breast cancer, compared with women who don't drink. And remember: The risk rises with the number of drinks consumed, so practice moderation.

Another lifestyle factor that's been linked to protection is exercise. Instead of sitting back and worrying about the implications of dense breasts, plan to eat right, drink sparingly (if at all), and get at least a half-hour of moderate exercise a day. You can't change your genes, but you may be able to walk away from risk.

(Submit questions to harvard_adviser@hms.harvard.edu.)

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