Dense breasts increase the risk of breast cancer and increase the chances of cancer going undetected by a mammogram.
The authors of the study, published in Annals of Internal Medicine, conclude that breast density should not be the sole criterion for deciding whether further imaging is justified, as not all women with dense breasts have high interval cancer rates.
Instead, women with specific types of dense breasts who have a high 5-year cancer risk should discuss the available options for additional screening with their doctors.
Dense breast tissue is composed of milk ducts, milk glands and supportive tissue and is a normal and common finding on a mammogram. Women are defined as having dense breasts if they have more dense breast tissue than fatty tissue.
As dense breast tissue appears as a solid white area on a mammogram, it can be difficult to see through and makes it more difficult for cancer to be detected using this imaging technique. Additionally, having dense breasts increases a woman's risk of developing cancer, although experts are currently unsure why.
The authors of the study report that 21 states have laws requiring that women be notified if they have dense breasts, with some recommending that they are advised to discuss additional imaging with health care professionals.
Although additional imaging can increase the chances of cancer detection, it can also increase the chance of a false-positive diagnosis. Certain forms of imaging can also be expensive or expose women to low levels of radiation.
The researchers set out to determine which combinations of breast cancer risk and breast density categories are associated with high interval cancer rates, and, therefore, determine which women with dense breasts would benefit from additional screening.
Data were analyzed from the Breast Cancer Surveillance Consortium (BCSC) mammography registries from 2002 to 2011. This period included data for 365,426 women aged 40-74 undergoing a total of 831,455 digital screening mammography examinations.
Breast density was defined using Breast Imaging Reporting and Data System (BI-RADS) breast density categories. The categories of density are "almost entirely fatty," "scattered areas of fibroglandular density," "heterogeneously dense" and "extremely dense."
Over half of women with extremely dense breasts not at high risk of interval cancers
The researchers found that over half of the women with extremely dense breasts (52.5%) did not have a high risk for interval cancers - defined as invasive cancer detected within 12 months of a negative screening mammography.
Rates of interval cancer were highest among women with both extremely dense breasts and a 5-year breast cancer risk of 1.67% or more (as calculated by the BCSC), or women with both heterogeneously dense breasts and a 5-year breast cancer risk of 2.5% or greater.
High rates of false-positive results were also found on digital mammography among women with heterogeneously dense breasts and a 5-year breast cancer risk of less than 1.67%.
The authors note that their study is limited by not assessing the benefits of additional imaging. Taking into account their findings, however, the authors conclude that not all women with dense breasts were at a high enough risk to justify considering additional screening.
"BCSC 5-year risk combined with BI-RADS breast density can identify women at high risk for interval cancer to inform patient-provider discussions about alternative screening strategies," state the authors.
In an accompanying editorial, Dr. Nancy C. Dolan and Dr. Mita Sanghavi Goel, of Northwestern University in Chicago, IL, suggest that federal legislation should focus on identifying women at high risk for interval breast cancer, rather than additional screening for women with dense breasts.
Earlier this month, Medical News Today reported on new data from the Centers for Disease Control and Prevention (CDC) revealing that many adults in the US are failing to undergo the recommended screening tests for breast cancer. According to the report, around 1 in 4 women in the US are not up-to-date with breast cancer screening.