How Does the Medication Work?Capecitabine is a unique chemotherapy medication. In the body, it is transformed into 5-FU (fluorouracil). Fluorouracil is a chemotherapy medication that is administered intravenously (through an IV). Fluorouracil cannot be given by mouth because it does not absorb well from the digestive tract into the body. Capecitabine was developed as a way for fluorouracil to be given orally. When the medication is taken by mouth, it is easily absorbed into the body. The body then transforms it into fluorouracil, providing all the benefits of fluorouracil without the need for an IV.
Fluorouracil works in at least two different ways. It interferes with a cell's ability to make new DNA (molecules that contain the cell's genetic information). In order to multiply, cells need to make new DNA. By interfering with DNA production, fluorouracil stops cells from multiplying. Enzymes in cells also mistakenly use fluorouracil when building important parts of the cell that are responsible for making proteins, which causes these parts to stop functioning.
Together, these two actions can cause permanent damage to cells, including healthy noncancerous cells. However, cancer cells divide more rapidly, producing more DNA and proteins and are, therefore, more affected by capecitabine. Also, cancer cells often have higher levels of the enzyme that transforms capecitabine into fluorouracil, which helps this medication have a greater effect in cancer cells compared to normal cells.
Clinical EffectsSeveral studies have looked at the effects of capecitabine for colorectal or breast cancer.
One study looked at using the drug for the adjuvant treatment of colon cancer that had spread to at least one lymph node. Adjuvant therapy for colon cancer is treatment that follows colon cancer surgery (with or without radiation). It is given to help prevent the cancer from returning. These studies compared capecitabine to a combination of fluorouracil and leucovorin. After three years, up to 66 percent of those taking capecitabine remained cancer-free, compared to 62.9 percent of those taking the fluorouracil and leucovorin combination.
Studies have also shown that capecitabine is better than fluorouracil plus leucovorin for metastatic colorectal cancer (colon cancer or rectal cancer that has spread to other parts of the body). More cancers responded to capecitabine than fluorouracil/leucovorin.
One study looked at adding capecitabine to docetaxel (Taxotere) for people with metastatic breast cancer (breast cancer that has spread to other parts of the body) who had already tried other chemotherapy medications called anthracyclines. This study showed that adding capecitabine increased the time to progression. "Time to progression" is a medical term that means from the time that the cancer is treated until the disease starts to get worse, such as when the cancer spreads (metastasizes) or the tumor increases in size. Also, those taking capecitabine and docetaxel survived an average of 442 days, compared to 352 days for those just taking docetaxel.
Another study looked at using the medication alone to treat breast cancer in people who had not responded to paclitaxel (Onxol, Taxol) and an anthracycline chemotherapy medication. In this study, capecitabine caused significant shrinking of the cancer in at least 25.6 percent of people.