Breast density is a breast imaging term that is assessed at the time of the mammogram. Increased breast density means having a higher proportion of parenchymal breast tissue (breast glands, ducts and supportive tissue) relative to fatty breast tissue. 

On the mammogram, very dense breast tissue appears white while fatty non-dense tissue appears black. Increased density is associated with younger age, lower body mass index (slimmer women) and women who take hormone therapy for menopause.

Is breast density on it's own a risk factor for breast cancer? Some specialists say yes, and some say no. In my opinion, the high breast density masks or hides breast cancer rather than increases the risk. I believe that density is just a surrogate marker, possibly one of the amount of active breast tissue.

Why do I think so?

1. There is an association of extreme (very high) breast density with higher rates of cancer in Western countries. However, an individual's personal risk factors and family history can affect the risk level.

2. This fact does not apply to Asia. Asian women (who live in Asia) have much higher rates of increased breast density, but much lower rates of breast cancer. When they move to Western countries, though, their rates of cancer increase and become similar to the Caucasian population's while their breasts still have increased density.

3. Obese women have higher rates of breast cancer, but lower breast density in general.

Is knowing your breast density important?

Yes, it is. At least for women living in Western countries. And breast density is important for breast screening intervals in certain women.

If you have densities 1 or 2 and normal/average family risk of breast cancer, you can continue with getting breast screening mammograms every two years. However, if you have density four (high density) and increased risk, as well as you are pre-menopausal, I suggest having yearly mammograms (preferably tomosynthesis, which is 3D mammogram). Depending on your family risk, you may also benefit from MRI or breast ultrasound. 

My advice to those concerned about the density of their breast tissue is to talk to their doctor about their family risk and personal circumstances, as they may benefit from having breast screening more often.