Correlation of Genomic Variation in Enzymes Responsible for Metabolism of Capecitabine With Drug Metabolism

Capecitabine, PK Testing, and DNA Analysis: Capecitabine is designed to interfere with the growth of cancer cells, which may cause the cells to die. It is cleared from the body by certain proteins (which are made from DNA--the gene material of cells). Some patients have changes in these proteins that increase or decrease the rate that capecitabine is cleared from the body. Researchers will use pharmacokinetic (PK) testing and DNA analysis to learn how capecitabine is cleared from your body. PK testing measures the amount of drug in the body at different time points. Information learned in this study may help researchers decide the best doses of capecitabine for future patients with breast cancer. Screening Visit: Before you can start treatment on this study, you will have about 2 teaspoons of blood drawn for routine tests and to make sure that you are able to receive chemotherapy. This screening blood test will help the study doctor decide if you are eligible to take part in this study. Capecitabine Treatment: If you are found to be eligible to take part in this study, you will be given capecitabine by mouth on the day you choose to start this therapy. Your treating doctor will prescribe capecitabine at a dose that is appropriate to treat the cancer. You can choose the start date, excluding weekends, but will need to begin therapy in the morning of the day you choose. You will have treatment with capecitabine even if you do not participate on this study. PK Testing and DNA Analysis: You will have blood drawn (about 2 teaspoons each time) for PK testing and DNA analysis of capecitabine at certain times throughout this study. * For PK testing, blood will be drawn before your first dose of capecitabine, at 30, 60, and 90 minutes after the first dose, and then at 2, 6, 8, and 10 hours after the first dose. * For DNA analysis, blood will only be drawn before you receive the first dose of capecitabine. If your dose changes, these PK blood tests may need to be repeated. Length of Study: You will remain on this study for up to 6 months, unless the disease gets worse, you experience any intolerable side effects, or you decide to stop treatment with capecitabine. This is an investigational study. Up to 100 patients will take part in this study. All will be enrolled at M. D. Anderson.