Last year, OnCancer featured a Q&A about breast density and breast cancer risk with Memorial Sloan Kettering diagnostic radiologist Carol Lee that drew a large number of questions and comments from readers. Recently, we checked in with Dr. Lee again to discuss breast density in more detail and gain additional insights into the topic.
Does dense breast tissue merely make it more difficult to detect cancer, or does dense tissue actually increase breast cancer risk?
The 10 percent of women with extremely dense breasts have four to six times increased risk [of breast cancer] compared with women who have completely fatty breasts [the least dense]. However, most women fall between these extremes, and it is impossible to determine a woman’s level of risk based solely on a mammogram.
It is very important to understand that women with non-dense breasts also can develop breast cancer.
Could some of the increased breast cancer risk be caused by the need for a higher radiation dose during screening mammograms in order to penetrate dense tissue? Or could the higher risk be due to the fact that dense breasts simply have more breast tissue that can be exposed to radiation?
It is unlikely that the difference in radiation dose, if any, contributes to risk associated with dense tissue. Everything else being equal, the amount of extra radiation required during mammography of dense breasts is extremely small. In addition, the amount of radiation needed depends not just on breast density but also breast size. So it is possible that a woman with large, non-dense breasts could actually receive more radiation than a woman with small, dense breasts.
Are there any tests that are better than mammography for women with dense breasts?
Mammography is the only screening test that has been proven to decrease deaths from breast cancer. However, mammography is not perfect and some cancers will not be seen on mammograms. For women with dense breasts, ultrasound is often used in addition to mammography for further evaluation. Ultrasound, however, picks up many things that turn out not to be cancer but that may require further testing, including biopsy.
Sometimes magnetic resonance imaging [MRI] can detect a cancer in dense breasts that was not seen by mammograms or ultrasounds. However, MRIs also have drawbacks. They require the injection of intravenous contrast dye; like ultrasound they may give a false-positive reading, resulting in the need for additional testing or biopsy that turns out to be benign; and they are very expensive and not always covered by insurance. In general, MRIs are used in women at very high risk of breast cancer such as those with a known genetic mutation associated with the development of breast cancer. Every patient is different, and decisions about which type of screening test is advisable should be made after discussion with a doctor.
Does the increase in breast density that naturally occurs while a woman is breastfeeding interfere with the ability to identify abnormalities in the breast?
The accuracy of screening tests such as mammogram, ultrasound, and MRI is reduced during breastfeeding because changes in the breast during this period make cancers harder to detect. For routine screening, it is generally preferable to wait a few months after breastfeeding has stopped before having a mammogram or MRI.
Do African-American women tend to have denser breasts than women of other races, and could this contribute to delayed diagnosis and increased mortality among black women with breast cancer?
Overall, African-American women do not have higher breast density than women of other races, so this does not seem to be a factor in the higher mortality rates among this population of women. Other factors, such as decreased access to care and more aggressive tumor types, are more likely to be causing the discrepancy.
Does breast density change from one year to the next? Does it generally stay the same after menopause and throughout one’s lifetime? What might cause breast density to change?
It is common for breast density to decrease gradually with age. However, many women maintain the same breast density throughout their lives, and it is not possible to predict how one person’s breast density may or may not change. Many things can affect breast density, such as taking or stopping hormone replacement medicines or gaining or losing weight, but this is quite variable.
What should women do if they are told after a mammogram that they have dense breasts?
As I recommended in the previous discussion, women with dense breasts should talk to their doctors about their individual risk for breast cancer and together decide whether additional screening makes sense.