Why does the same cancer treatment not work for everyone with the same type of cancer?

Different subtypes. We are learning more all the time about genetic differences within the same type of cancer. For example, one gene in 20% of breast cancers predicts good response to an antibody treatment. Other breast cancers that are estrogen-receptor positive will respond to hormone drugs like tamoxifen. As we learn more, we hope that more cancer treatment can be personalized for each patient.