Local HER-O: A study of local therapy for the treatment of brain metastases from Human Epidermal Growth Factor Receptor Type 2 (HER2) positive breast cancer.

For patients who have Human Epidermal Growth Factor Receptor Type 2 (HER2) positive breast cancer, which has metastasised to the brain, the main treatment options for these brain metastases are Whole Brain Radiotherapy (WBRT), Stereotactic Radiosurgery (SRS) and Neurosurgery (NS). Sometimes, if the metastases are small and are not causing any symptoms, they do not require any immediate treatment and will be observed. The purpose of the study is to determine 1) How likely the tumour/s are controlled after treatment with local therapies Neurosurgery (NS) and/or Stereotactic Radiosurgery (SRS) and 2) How likely is it that other tumours develop at new sites in the brain when no Whole Brain Radiotherapy (WBRT) is given. The local treatment offered will be determined by the patients doctor in consultation with the site multidisciplinary team and will be dependent on the size and location of the brain metastases. Each treatment will be performed by the specialist in that field, i.e. neurosurgeon and/or radiation oncologist. Neurosurgery: The decision whether or not to recommend neurosurgery will be made independently of this research study. The surgery may be performed up to 6 weeks before participant being registered on the trial or up to 4 weeks after registration. The complexity and length of the surgery depends on the size and location of the tumour(s). Sometimes stereotactic radiosurgery is required to be delivered to the cavity left after the metastasis has been removed (also known as a cavity boost). Timing of Cavity SRS is at the discretion of the treating team. SRS cavity boost must be given after registration and can be given up to 8 weeks after NS resection. Stereotactic Radiosurgery: If the participant will be receiving stereotactic radiosurgery (either alone or in combination with neurosurgery), the Radiation Oncologist will organise for the participant to have a Radiotherapy planning. Treatment is to commence within 4 weeks of study registration. The size, number and location of the brain metastasis will determine the dose and fractionation schedule of radiotherapy. Single metastasis, smaller than or equal to 2cm, may require 1 fraction. Alternately, multiple metastasis, metastasis in the brain stem, or those bigger than 2cm will required multiple fractions to treat. The dose range for the study is 20Gy/1 fraction to 24Gy/3 fractions. Each fraction is given on a separate day.