My neuro-oncologist shared the ASCO 2011 Graded Prognostic Assessment for Brain Metastasis that includes breast cancer and breaks out HER2 positivity (no differentiation between hormonal status though).
The 2011 report used an original dataset spanned 1985-2007, so it predates Perjeta and some other more current treatments, plus some HER2 patients didn't receive Herceptin until it was made publicly available.
ASCO Graded Prognostic Assessment for Brain Metastases [Journal of Clinical Oncology, January 2012]
http://jco.ascopubs.org/content/30/4/419.full
Figure 1 includes the scoring table, midway are the patient characteristics. I scored 90-100 for
KPS but you might need to consult with your oncologist about what that is for you; it has to do with functioning level versus impairments. You see which column your diagnosis falls into and then you use the prognositc factor to the right under the patient score (0,.5,1.0,1.5,2.0) to see what your final total and then there is a key at the bottom of the table for median survival.
This recent report on HER2 Brain mets using the above validates this scoring method.
Graded prognostic assessment (GPA) of HER2 positive breast cancer patients with brain metastases. [2015]
http://meetinglibrary.asco.org/content/145612-156