Hi M, it's also worth checking out this resource from the College of American Pathologists:
Understanding a Cancer Diagnosis: Invasive Ductal Carcinoma
Invasive and Infiltrating are the same in this case.
The report discusses what your pathologist is looking for and how he or she made a diagnosis of IDC.
PJ Hamel has also written a great FAQ on IDC, which is a good starting point. Let us know if these resources help and if you find other good ones.
Thanks and good luck.
Sarah