<qa>  What is the second most common cause of brain metastases?Breast cancer is the second most common cause of brain metastases. Overall survival after the development of brain metastases tends to be poor 6-8 months. Over-expression of Human Epidermal Growth Factor Receptor 2 HER-2neu, negative estrogen receptor, and young age at diagnosis seem to be indicators of high risk for brain metastases. Temozolomide may be a good candidate for prophylactic chemotherapy because of its ability to cross the blood-brain-barrier, achieving high concentrations in the central nervous system CNS. 