The role of the immune system in successful breast cancer treatment has until been unknown. Presented in abstract form at the June, 2014 meeting of the American Society of Clinical Oncology is a mind-bending study by Dr. Edith Perez of the Mayo Clinic in Jacksonville and others that shows that successful treatment with Trastuzumab (Herceptin) requires several activated immune function genes. The group identified 10 biologic processes controlled by 87 genes that were required for Herceptin to work. As background, about a quarter of breast cancers overexpress the HER-2 gene and those cancers tend to be more aggressive. Herceptin was developed to block the activity of that gene and is highly beneficial for women whose tumors are HER-2 positive. This study identifies those women whose tumors are HER-2 positive who have a high probability of being helped by Herceptin and also identifies a group for whom Herceptin is ineffective and a waste of time. Since this drug is very expensive and potentially toxic to the heart, this information is important. Various investigators have then suggested that HER-2 negative tumors that share the same 87 mutations as described above might benefit from Herceptin, even though conventionally they are not supposed to. That proposal will have to be tested. Why is this so important? These data further characterize and explain why certain cancer treatments are effective and help refine the decision-making processes that Oncologists go through when designing customized treatments for patients. Also at the meeting was a declaration from Memorial Sloan Kettering Cancer Center that they hope to acquire the funding to completely analyze the DNA of tumors of all newly referred patients and plan their treatments around the mutations present in that DNA rather than by the type of tumor. This approach is truly revolutionary.