ERBB2 and breast cancer: Considering that trastuzumab is known not to cross the BBB (Pestalozzi and Brignoli, 2000; Stemmler et al, 2007) and that patients treated with trastuzumab show higher development of BM than patients not treated with trastuzumab, introduction of trastuzumab might not overcome the biological aggressiveness of HER2-positive breast cancer, but may affect the clinical features of BM by improving systemic extracranial outcomes.