August 26, 2013 | The blood brain barrier prevents many anticancer drugs from reaching areas of the brain to which cancer has spread and metastases commonly develop in multiple locations which further complicate current treatment options. Cellular therapy uses the T cells of the immune system, which have had their properties adjusted to kill breast cancer cells. In genetic therapy, cancer cells are often genetically modified (the gene is transmitted through a virus) and then killed by a 5-fluorocytosine. When these therapies are used in combination, studies show the greatest reduction of in metastatic brain tumor size than when used individually. OncologyNurseAdvisor