Despite breast density being recently declared by US researchers to be the most common risk factor to determine a woman’s chances of developing breast cancer during her lifetime, very few Australian women have any knowledge of the potential implications of breast density, let alone whether they themselves have dense breasts.
A landmark study completed at the University of California, San Francisco, in January 2017, has been an important step towards raising scientific and medical awareness of the impact breast density can have on a woman’s chances of developing breast cancer—yet there is still a way to go in raising public awareness.
The study, which concluded “dense breasts eclipse all other known breast cancer risk factors,” was based on the evaluation of the breast cancer risk of more than 200,000 US women. Specifically, it found having dense breasts was estimated to explain 39 percent of breast cancer cases in premenopausal women and 26 percent of cases in postmenopausal women. This elevated risk of breast cancer is attributable to two factors: i) the higher fibroglandular content of dense tissue, which creates a favourable environment for cancer development; and ii) the difficulty of detecting breast cancer in patients with dense breast tissue—both tissue and cancer appear white in mammograms.
To put these results in context, the University of California study also found that well-known factors commonly associated with breast cancer, such as a family history of the disease, accounted for less than 10 percent of breast cancer cases in the population. While family history (particularly in first degree relatives) remains an important risk factor, it is not common, only occurring in approximately 12 percent of the population. Compare this to the prevalence of high breast density, affecting an estimated 40 percent of women over the age of 40, which highlights the urgent need for a greater public understanding of this important risk factor.
A survey conducted last year in Australia by an independent market research firm, AMR, showed that only 23 percent of women, when prompted, recognised breast density as a risk factor, and only 10 percent were aware that breast density is a factor which makes detecting breast cancer using mammograms more difficult.
The implications for Australian women
This has important implications for Australian women, the majority of which are screened by routine biannual mammograms under publicly funded national breast screening programmes. Breast cancer screening using mammograms has been proven to save lives, with most estimates suggesting a reduction in mortality from screening of 20 to 40 percent. However, it is also known that approximately 40 percent of cancer present in women with extremely dense breasts will be missed by a standard mammogram programme. Overseas, women with high breast density are offered alternative screening techniques such as tomosynthesis or ultrasound, which provide much higher accuracy and success rates in the earlier detection of breast cancer, but at a potential risk of more false positives.
Aside from the risk of reduced sensitivity, given high breast density is also a marker indicating a woman is at a higher chance of developing breast cancer over her lifetime, it is important to identify these women so they can be offered increased screening and awareness opportunities as well as education about disease-prevention strategies. In fact, the recently released Tyrer-Cuzick 8 breast cancer risk assessment tool can be used to predict breast cancer risk, including, for the first time, a woman’s breast density.
So, how does a woman know if her breasts are dense? The Volpara solution
A radiologist interpreting a mammogram can assess breast density, but it is subjective and reliant on human input. BI-RADS and the visual analogue scale (VAS) are both visual methods where the radiologist observes the percentage of the breast that looks dense; interpretation however, can vary.
Volpara has developed software that provides an objective and quantifiable measure of breast density—rather than being based on visual opinion. This software uses algorithms to estimate the volumes of tissue in the breast. Unlike a mammogram, where the radiologist looks at the images and estimates the area of density as if the breast is two-dimensional, Volpara’s technology looks deep inside the breast to measure the absorption of x-rays in the breast caused by fibroglandular tissue. Thus, Volpara is looking at the true tissue, not the shadow of the tissue—and as such getting much more objective results.
Women in Western Australia are already offered a visual assessment of breast density by the screening programme, whereas sites such as Women & Breast Imaging in Perth, Dr Jones & Partners Medical Imaging in Adelaide, and shortly Sydney Breast Clinic offer true volumetric readings.
International trends
Overseas, there is growing awareness and acceptance of the role breast density plays in breast cancer screening. In March, Cancer Research Technology in London released the updated Tyrer-Cuzick Breast Cancer Risk Assessment Tool (TC8), which for the first time incorporates breast density as a risk factor. The Tyrer-Cuzik risk prediction model has shown superior risk assessment compared to other models and is widely used by leading international bodies in the US and Europe that make recommendations for screening and breast cancer prediction, such as the American Cancer Society and the National Institute for Health and Care Excellence UK. Significantly, the TC8 tool is now being used by insurers in the US to qualify women at an elevated risk of developing breast cancer for additional screening procedures such as breast MRI. Volpara’s highly regarded VolparaDensity software is now the recommended breast density input to the Tyrer-Cuzik model.
Clearly, breast density awareness is a conversation Australian women need to have, and groups such as INFORMD are starting that conversation. In the US, 30 states now require that a woman is told her breast density after each screening.
We believe Australian women should have access to the latest and most accurate knowledge so that those with greater risk can be managed more effectively, improving patient outcomes should they develop one of the most invasive cancers affecting women worldwide.
