Breast density and breast cancer: What you don’t know can hurt you

Given that one in eight Canadian women will develop breast cancer in their lifetime, and one in 31 will die from it, having reliable information on prevention and screening is crucial.

In 2013, Angelina Jolie publicly disclosed that she had undergone a double mastectomy. This created wider awareness of the role played by genetics, and specifically the BRCA1 and BRCA2 gene mutations, in incidences of breast cancer. Most Canadian women have heard about getting regular mammograms, and know that smoking is a huge risk factor. Drinking alcohol is also high on the list, as are things that are significantly less controllable — birth weight, anyone? Breast density, however, is a less well-known risk factor, and is only beginning to receive adequate publicity in Canada.

What are the risks?

If you have dense breasts, you are four to six times more likely to develop breast cancer than a woman who is lowest on the breast density scale. This is true even if you’ve never had a family member with breast cancer. Given how significant the correlation between the two is, you’d think that it would be part of the conversation your doctor has with you when they check your breasts, right? Unfortunately, that depends on where you live.

Different provinces have different rules, and in many places in Canada, your doctor may not even know if you have dense breasts. And if your doctor doesn’t know, then how would you? And that’s the thing, you most likely don’t know. Having dense breasts is both normal and common. You can’t tell just by touching them, or by looking at them.

So what exactly is a dense breast?

Simply put, it’s a breast that has more glandular and fibrous tissue, as opposed to fatty tissue. More specifically, there are four categories of breast density, ranging from A (fatty) to D (extremely dense). In between, you have B (scattered areas of density), and C (heterogeneously dense). The size, shape, or the way a breast feels, has nothing to do with its density. The only way to know, is by having a mammogram.

Does breast density affect mammogram accuracy?

Not only do they have a higher risk of breast cancer, but women with dense breasts are also less likely to have their cancers spotted. While fatty tissue shows up as dark on a mammogram, the dense areas of a breast show up as white. Guess what else shows up white on a mammogram? Cancer. This means that in dense breasts, the radiologist is less likely to see a tumour if one is present. Many women think that once they’ve had a mammogram come back as negative, they are free and clear.

If you have dense breasts, you may want to consider additional screening if you receive a negative mammogram — research has shown that additional ultrasound screening can detect previously undetected cancers on a mammogram.

Additionally, women with dense breasts are more likely to develop interval cancers. What’s an interval cancer? Well, it’s a cancer that has appeared in the interval since your last mammogram. In some cases, this may be because the cancer wasn’t spotted initially.

How do I mitigate my risk?

Well for starters, women 40 and over should speak to their doctors about their risk factors for breast cancer, and women over 50 should be having mammograms every two years. Every woman should be aware of factors that increase the incidence of breast cancer. In the meantime, working towards living a healthier and smoke-free life should be at the top of everyone’s list.

And you should talk with your doctor about your breast density. Ask if they know about the link between breast cancer and breast density, and ask them to check with the radiologist to figure out where you fall on the spectrum. If it turns out that you have dense breasts, discuss your lifestyle and family history with your doctor, and talk to them about screening with ultrasound. Knowing about your breast density could save your life.