Though brain metastases are a risk in all patients with breast cancer, those with HER-2 overexpression are at significantly greater risk. One series estimated a 30% incidence of brain metastases in this population, while another study found an incidence of approximately 40%. Traditional systemic therapies do not cross the blood brain barrier to any significant degree or at all, but radiation treatment can be effective in the treatment of intracranial metastases.

The rationale for PCI is that the brain is a sanctuary site where cancer cells can remain inaccessible to chemotheraphy and agents such as trastuzumab due to the blood brain barrier, which prevents potentially harmful chemicals such as chemotherapy agents and antibodies such as trastuzumab from reaching the brain. Decreasing the incidence of brain metastasis with acceptable effects on neurocognitive function would be a significant improvement in the care of patients with MBC.

Inclusion Criteria:

• Female with HER2-positive disease
• 18 years of age or older
• ECOG greater or equal to 2
• Life expectancy greater or equal to 6 months
• Able to complete self administered quality of life evaluations and neurocognitive testing
• Willing and able to comply with study instructions and commit to all clinic visits for the duration of the study
• Women of child-bearing potential must have a negative serum pregnancy test at screening and a negative urine pregnancy test at the baseline visit and must use highly effective birth control during study
• Signed informed consent form

Exclusion Criteria:

• Current malignancy in the brain, as determined by screening MRI/CT done no more then 6 weeks prior to study treatment with PCI
• Chemo or radiation planned during the period when patients will receive study treatment with PCI
• Prior radiotherapy of the brain
• Prior stroke or brain hemorrhage in the 6 months prior to screening
• History of neurological/psychiatric disorders, including psychotic disorders or demential, or any other reason, which may affect neurocognitive assessment
• Inadequate renal function
• Other known previous or concomitant serious illness or medical condition that may interfere with participation in the study