Safety Study of a New Schedule of Capecitabine and Docetaxel to Treat Cancers

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.

Our hypothesis is that capecitabine and docetaxel interact with each other, because capecitabine primes the pro-death machinery of the cell by increasing the ratio of death-promoting proteins to death-inhibiting proteins. Cells are more susceptible to killing by docetaxel when the pro-death machinery is activated by capecitabine.

This is a safety study to find the highest dose of capecitabine that can be given safely for 14 days, in combination with docetaxel given at a fixed dose on day 8. Once this dose of capecitabine has been determined, an additional nine patients with tumors that can be biopsied will be treated at this dose, and levels of capecitabine, its byproducts, and docetaxel will be measured in the bloodstream. Biopsies of tumors will also be taken before and after the docetaxel is given, and the levels of pro-death and anti-death proteins will be measured.