breast density

I have always had very dense breasts. And on my most recent annual  mammogram, I noticed on my mammogram report that it says "40 percent fatty replacement." What does this mean? Thank you very much!-Miracat

[CCF-RN,MSN-JS]

Dear Miracat, As we age the ratio of breast tissue (which on a mammogram is dense) to fat changes.  The amount of fat tissue increases and dense breast tissue decreases.  This is why mammograms are a better screening tool as we get older - 40's, because we can pick up abnormalities easier as they are not obscured by the natural density of the breast.

[miracat]

Thank you so much for taking the time to help me understand this. Does this mean, then, that because the report says "40 percent fatty replacement" the rest of the material in my breast is density? What is the density made up of and is it harmful? Thanks again!-Miracat