Check out The Cancer Genome Atlas, specifically their Analytical Tools page: https://tcga-data.nci.nih.gov/tcga/tcgaAnalyticalTools.jsp. TCGA collected digitized pathology slides on ~1,000 breast cancer patients (look for the TCGA-BRCA group). The Berkeley tool (http://tcga.lbl.gov/) and the Cancer Digital Slide Archive (http://cancer.digitalslidearchive.net/) would probably be of most interest to you.
The Cancer Imaging Archive also has corresponding radiology imaging on the same patients if that's of any interest: http://www.cancerimagingarchive.net/.