I've read about gliadel wafers being used for breast cancer brain mets successfully before. Given that adjuvant chemo is not standard of care for the brain as the first site of metastases and due to my own observations that a) they wait until lesions are large before recognizing them, b) resectioned tumors via craniotomy increases the risk of the spread of BC brain mets and c) the expectation is not "if" the lesions come back but more a matter of when then adding in chemo agents directly into the tumor bed makes sense. We know that targeted therapies work best against HER2+, especially in combo with a cytotoxic agent, perhaps lumber puncture administration of IT Herceptin into the spinal fluid would be a good companion.
This is a good read:
Gliadel for brain metastasis
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3656564/