Addt'l mammo views vague

My screening mammogram came back as follows: breast tissue is heterogeneously extremely dense. There is increased density in the upper half of the right breast seen on the MLO view since the previous exam of 2000. This probably represents summation shadows. Repeat MLO and 90 degree mediolateral projection and spot compression views to help exclude underlying neoplasia. Left breast is unremarkable.
They called me back in for additional views which show the following: additional views of the right breast show the area to compress out relatively well. As this does represent an area of asymmetry, suggest follow up in six months to confirm stability. Assessment is a Category 3 (probable benign findings).
Is a six month follow up all I need or should they have requested an ultrasound as well? I really don't understand the results.

[Amy1973]

You should just call back and ask if you should be worried.  I would also say that If I had something that read (probable benign findings) I would aks to have it looked at in more detail - us or MRI.  I wouldn't settle with problable.

Good luck!