Growth in density

I had my first mammogram in 2009, I just had my mammogram for this year. My Breast Health Nurse called me to tell me they want me to come in for another look and probably an ultrasound. There was a density present at my first mammogram that has grown in the past year and they want a clearer look. What does this mean and should I be worried? My paternal grandmother and my paternal aunt both had breast cancer. My aunt survived but my grandmother did not. This all leaves me pretty terrified and a week till I go back for my "clearer look". Can you please help me?

[Cleveland Clinic]

Dear ChelleSue:  It is not uncommon for a mammogram to detect an abnormality that will require additional views.  Sometimes it is as simple as tissue folding over on itself and it resolves with spot compression.  If the abnormality remains on further views, then additional testing, such as ultrasound, may be done to determine if the mass is cystic or solid.  Each test gives a piece of information and would determine the next step.