Each year in the United States over 30,000 patients with breast cancer are treated with a class of drugs known as the anthracyclines. The anthracyclines are one of the oldest and most effective chemotherapies for breast and other cancers. However, some patients do not benefit from this therapy for reasons that are not understood. Moreover, because the anthracyclines target TopoII isomerase (TopoII), a remarkable protein that is vital for normal cellular functions such as untangling DNA, they can have serious side effects. Recently, we have found that we can predict whether cancer cells will respond to TopoII inhibitors based on their genomic profile. Our over-arching goal is to spare patients treatment with this highly toxic class of drugs if they will not benefit from their use. By performing a simple genomic test on the patient’s tumor sample obtained at the time of diagnosis, we aim to predict which patients will benefit from anthracyclines and thereby inform treatment decision-making. In this manner, treatments can be personalized so that patients receive the best possible current therapy to treat their specific tumor, while being spared ineffective drugs and their side-effects.