Pharmacology and clinical status of capecitabine.

Capecitabine (Xeloda) is a new, orally administered, enzyme-activated fluoropyrimidine carbamate designed to generate high levels of fluorouracil (5-FU) in tumor cells. Selective tumor activation of 5'-deoxy-5-fluorouridine, the last enzymatic step of a three-enzyme process, is catalyzed by thymidine phosphorylase, a tumor-associated angiogenic growth factor. Since levels of thymidine phosphorylase are often higher in tumors than in surrounding normal tissues, this stepwise process provides tumor selectivity and potentially decreases toxicity to normal tissues. Preclinical studies show that capecitabine has significant activity against a variety of tumor types when used as monotherapy and in combination with other chemotherapeutic agents. Capecitabine is currently approved for the treatment of patients with metastatic breast cancer resistant to paclitaxel (Taxol) and in whom further anthracycline therapy is contraindicated. It has demonstrated efficacy in patients with advanced colorectal carcinoma, and studies are ongoing in other tumor types.