Capecitabine and Gemcitabine in Patients With Metastatic Colorectal Cancer

This study is for patients with colorectal cancer that has spread and has increased in size after standard treatments. This study is being done to find out how long it takes their tumors to grow after treatment with the chemotherapy drugs capecitabine and gemcitabine. Capecitabine is a chemotherapy drug that has been approved by the FDA for the treatment of colorectal cancer. We are adding another drug (called gemcitabine), which is approved by the FDA for the treatment of cancer of the pancreas to see if the ability of capecitabine to shrink tumors can be improved by adding gemcitabine. The side effects of the combination will also be evaluated. Another purpose of this study is to measure the levels of certain substances that affect how the body reacts to the chemotherapy agents in cancer cells (in the tumor). In addition, the genes (which are the cell's blueprint for these substances) will also be evaluated in the blood.