How breast density affects your risk for cancer

If you have ‘dense breasts,’ tumour detection can be difficult. Here’s what you need to know to protect yourself from breast cancer

How breast density affects your risk for cancer

Source: Best Health Magazine, October 2012; Image: iStock

Research is showing that women with dense breasts can be at a grave disadvantage in the diagnosis of breast cancer during routine mammograms. Dense breast tissue’comprised more of the connective milk-duct and milk-gland tissue than of fat’shows up white on a mammogram, as do some tumours, so spotting problems can be like ‘trying to find a snowflake in the snow,’ says Dr. Sharon Bean, a radiologist with VIP Breast Imaging, a private clinic in Toronto. ‘The tissue basically masks the tumour,’ she explains.

Just to make it a double whammy, research shows that cancer occurs more often in women with dense breasts than in those with little or no density, making it a true risk factor. A 2007 study by Toronto’s Princess Margaret Hospital’University Health Network (with the Ontario Breast Screening Program and the Screening Mammography Program of British Columbia), found that women with dense breast tissue are five times more likely than women with little or no density to be diagnosed with breast cancer. That makes it a bigger risk factor than having a mother or sister with breast cancer (which almost doubles your risk).

Ann Crawford, 56, of Hamilton, Ont., can attest to the fact. Crawford had a clean mammogram in January 2009. But a few months later in late spring, she noticed dimpling on her left breast, below the nipple area. ‘I wasn’t worried about it,’ she says. ‘I’d had my routine mammogram and I have no family history of breast cancer.’ But in August, while on a routine visit to her doctor, she happened to mention the changes. Her doctor examined her and referred her back to the breast screening centre that had given her the mammogram. They gave her a breast ultrasound, which showed that there, hid-den in the dense tissue of Crawford’s breast, was a small tumour that the mammogram had completely missed. Despite the tumour’s small size, some of her lymph nodes were affected, too.

How can you tell?

Unfortunately, you won’t know by looking at yourself, or by feeling yourself, if you have dense breasts, says Dr. Norman Boyd, senior scientist at The Campbell Family Institute for Breast Cancer Research at Princess Margaret Hospital, and lead author of the Princess Margaret study. ‘The only way of knowing is with imaging’a routine mammogram, or magnetic resonance imaging [MRI].’ Even then, you may not be told your breasts are dense.

In Canada, doctors aren’t required to share information about breast density. Bean routinely notes the presence of dense breast tissue in her mammography reports, pointing out that ‘[density] lowers the mammographic sensitivity, potentially masking a tumour.’ But making such notes is not standard for all radiologists, she says. And even when radiologists do issue the warning on a report sent to a family doctor, the news doesn’t always get to the patient. The result: Despite the fact that about 20 percent of women have very dense breasts, most are not even aware of it.

In the U.S., there’s a move afoot to change that. The states of Connecticut, Virginia, Texas and New York recently passed bills requiring healthcare professionals to notify women when routine mammograms show their breasts are dense, so they can seek additional testing if they wish. Other states, including California, are expected to follow suit. In Canada, the Senate adjourned on the second reading of a similar private member’s bill (Bill C-314) in June 2012.

Some doctors say they don’t want to cause their patients undue anxiety, but that omission may give women a false sense of security, particularly when they have just undergone a routine mammogram. ‘Women with very dense breasts were 18 times more likely to find cancer in their breasts within the first year after a mammogram, according to the Princess Margaret study,’ says Boyd. ‘This suggests that the mammogram didn’t pick it up.’

He advises asking your doctor if you have dense breasts. ‘They’re more likely to pay attention if they know there is a demand  for the information.’ And note that if your mother or sister has dense breasts, there’s  a higher chance you do, too. ‘Density appears to be largely inherited,’ says Boyd.

That said, don’t stress unduly if you find out you do have dense breasts; just be conscious it is a risk factor. ‘You need to be a little bit vigilant,’ says Boyd. That means getting yourself to the doctor if you note any changes in your breasts, including lumps, discharge from the nipple, alterations in the shape of the breasts, dimpling or pulling-in of the skin, and variations in skin texture (perhaps thickening or roughness).

In addition, advises Boyd, you might want to think twice about combined hormone replacement therapy (HRT) containing estrogen and progestin. A 2010 study published in the Journal of Clinical Oncology found that post-menopausal women with high breast density are at an increased risk of breast cancer, and that this risk is heightened when using HRT. ‘If you can’t avoid HRT, take it for the shortest possible time,’ suggests Boyd. ‘When you stop the therapy, density decreases again.’ If you have dense breasts, as well as other risk factors, such as a family history of breast cancer, your doctor may consider putting you on the drug tamoxifen as a preventive measure, as it ‘decreases density and also decreases breast cancer risk,’ says Boyd.

What’s next?

In the meantime, research is ongoing into additional screening tests that might increase the likelihood of detecting tumours in dense breasts. Doctors say mammograms aren’t about to go away’they still catch the majority of cancers. But some tests, such as breast ultrasound and MRI, may be added for high-risk individuals.

That said, unless there’s a very good reason to believe cancer or any clinically palpable mass might be present, you’re unlikely to be offered such a test through your provincial healthcare plan. If you can get to the Toronto area and you’re willing to fork out $300, there are currently two private clinics in Canada that offer 3-D breast ultrasound using the state-of-the-art ABUS machine; a location in Vancouver is set to open this month (October). There are other private clinics across the country that offer breast ultrasound and MRI’for further information, see’as well as breast thermography. These tests seem to be of value in isolating tumours in dense breast tissue when used in addition to mammograms.

‘When there are reasons to do it, ultrasound screening is important for peace of mind,’ says Crawford. In 2009, she underwent a lumpectomy followed by chemo, then radiation for breast cancer in 2010. But despite her most recent clean mammogram in the fall of 2011, in the spring of 2012 she again noticed some dimpling, this time on her right breast. During a routine appointment with her oncologist, she asked for an ultrasound, just in case. But the specialist refused despite Crawford’s history. When visiting her family doctor for an infected bug bite in June, Crawford reported on the dimpling of her breast and her doctor ordered an ultrasound for Crawford. Fortunately, it showed only an enlarged milk duct.

Nonetheless, says a relieved Crawford: ‘If there’s one thing I’ve learned, it’s that you have to be proactive about your health.’

This article was originally titled "Hide and seek" in the October 2012 issue of Best Health. Subscribe today to get the full Best Health experience’and never miss an issue!