Question: What is the difference between the various systemic therapies, and how is the decision made about which ones should be used in a given patient? What factors are involved in making the decision? What kind of doctor should be making the decision?
Answer: Breast cancer therapy involves three different types of therapies normally: surgery, radiotherapy, and what we call 'systemic therapy.' The decisions about systemic therapy, which is basically drug therapy, are largely overseen by the specialists that we call 'medical oncologists.'
In the breast cancer field, we have several different kinds of systemic therapies; we have available to us chemotherapies -- the types of therapies that patients traditionally think about when they think about cancer therapy -- and we have available to us hormone therapies -- those that target the estrogen receptor in its pathways, things like tamoxifen and the aromatase inhibitors -- and increasingly, we have available to us certain kinds of biological therapies. The ones that are available currently are two drugs that target the HER2 pathway: the drug 'trastuzumab' (or Herceptin) -- a monoclonal antibody -- and a pill type of therapy called 'lapatinib' (or Tykerb). We are also increasingly seeing other types of biological therapies that are coming on board. For example, the monoclonal antibody called 'bevacizumab' (or Avastin) - an antibody that tries to tackle a protein that is important in the process of new blood vessel formation, a critical property for cancer cells as they grow and spread. So this is the armamentarium that doctors and patients have to work with for the systemic therapy of breast cancer.
When we think about how we would use these drugs, we usually use them to do three things: one -- most importantly, is to decrease the possibility that microscopic breast cancer cells will cause problems in the future; or, in the instance of a woman who already has metastatic (or spread) breast cancer, to try to reduce the burden of the breast cancer cells. We also will sometimes use them to try to reduce the chance of recurrence of the known breast cancer within the affected breast. And some of these drugs will also contribute to reducing the possibility that the patient will develop a new, second, unrelated breast cancer in the other breast in the future.
Now how to apply these is a very, very complicated science. The application of these drugs is based on the results of many decades of clinical trials, and many such clinical trials are going on now, as we try to perfect the use of these drugs and other drugs that will come in the future. But usually a patient and a doctor will sit together and they will think about: what the patient's outlook is with regard to this breast cancer; what is her prognosis if she undertook no therapy.
They will then look at the features of the cancer: estrogen receptor, progesterone receptor, HER2 protein, lymph node involvement, tumor size, the histologic grade, all of these kinds of features. And they'll get some sense of what the possibilities are for the use of therapy -- which therapies might be appropriate, what would be the potential advantages of the therapy, how might they change breast cancer outcomes in the future, and of course, we would also want to think about the toxicities (the side effects of therapy). So all of these are complicated discussions that involve very much an education of the patient about the features of her breast cancer - the outlook with her breast cancer, what the positive benefits of therapy might be, and what the downsides of therapy are - so that she and her physician can make a decision about how the balance plays out for her.