Brain Mets - answered our question?

Sorry if I have missed any posts in the last few days but between critical illness for pets and my torso MRI, Breast MRI and Brain MRI I have been busy.
Janelle and I have been wondering if it is possible to get Brain mets while on Herceptin. Onc told me to come in today (3/25) for results. Did not even get the results of the torso scan or the Breast scan since he was so stunned by the Brain MRI. He would never have scheduled the test as I don't have any symptoms but I insisted. There are so many mets that they can't be counted and he is stunned that I am not showing side effects. Apparently most would be having seizures etc. with this many, especially this size. Already had my first treatment of whole brain radiation. Astoundingly I feel as good as I always have! Still planning to continue Herceptin. Is this because I have stage IV Lobular cancer or are we all this vulnerable?