The combination of capecitabine and docetaxel is given to treat several different types of cancer. Capecitabine is usually given by mouth for 14 days, and docetaxel is given IV on the first day of capecitabine. The effects of changes in the schedule of the combination of docetaxel and capecitabine has been examined in human breast cancer cells. A capecitabine by-product was given orally to breast cancer-bearing animals for 14 consecutive days. Docetaxel was given IV at a variety of times between days 1 and 15. The greatest reductions in the volume of the cancer were seen when animals were treated with docetaxel between days 6 and 10. In two other breast cancer models, the maximal degree of delay in growth of the tumors was achieved when the animals were treated with docetaxel on day 8 of a 14 day course of capecitabine. The extent of tumor response was not explained by changes in tumor levels of the enzyme thymidine phosphorylase, which is thought to be the mechanism behind the interaction of capecitabine and docetaxel. In the breast cancer cells, capecitabine increases the level of proteins which promote death of cancer cells, and it inhibits the levels of proteins which block death of cancer cells.