Breast-density announcement raises concerns, confusion
Health Minister Adrian Dix’s announcement that B.C. will be the first province to notify women if they have dense breasts after screening mammograms, and may therefore be at higher risk of cancer, has led to some concerns and confusion about how the information should be used.
Advocates have long pressed cancer authorities and governments to share such information with women. It has always been collected by screening programs, and dense breasts are one of a number of factors raising the risk for breast cancer.
In B.C., dense breasts are fairly common — 106,000 women out of 255,000 screened in 2017 had the highest levels of density — and while more knowledge in the hands of patients is always empowering, there are many questions about how the health-care system might cope with a deluge of requests from women who may demand supplementary testing along with their mammograms, or when they discover a so-called interval lump weeks or months after their routine, normal mammograms.
Supplementary tests include ultrasounds, MRI and digital tomography imaging, all of which may be more effective at finding tumours in dense (fibrous, glandular) tissue, as opposed to more fatty tissue. On mammogram X-rays, tumours appear as white masses, but so does dense tissue. Therefore, dense tissue can obscure or mask tumours, which is why there are higher rates of advanced breast cancers diagnosed in the intervals between screening mammograms among women with dense breasts.
About 3,500 women in B.C. are diagnosed with breast cancer each year. It is the most common cancer in women. On its own, breast density is not reliable as a sole predictor of breast cancer risk, but among women aged 40 to 74, those with the highest density have about double the risk of being diagnosed with breast cancer in the intervals between their screening mammograms.
Other risk factors include family history, menopausal history, reproductive factors and body mass index.
Dr. Paula Gordon, the radiologist who is medical director of the Sadie Diamond Breast Program at B.C. Women’s Hospital, said tumours found in the interval periods between mammograms are often larger and often have already spread to the lymph nodes. Such patients require more radical treatment and face a poorer prognosis.
“These women are more likely to need mastectomy (rather than lumpectomy), need axillary (lymph node) dissection rather than just sentinel node biopsy ... and are more likely to need chemotherapy.”
Based on an American model, an additional three to four cancers per thousand women screened are expected to be detected as a result of breast density information being known and used with the imaging techniques.