Capecitabine is a unique chemotherapeutic agent for two reasons. It is the only oral chemotherapy drug available to treat breast and GI malignancies, making it convenient for patients. In addition, whereas all other cytotoxic chemotherapy agents can be administered for only a few months at a time because of development of cumulative toxicities, capecitabine can be continued for many months to years if toxicities can be managed. However the optimal dosing schedule of capecitabine is not known.