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Why isn't my chemotherapy working?

My doctor tells me my chemotherapy isn't working any more and my cancer is growing. Why is this?

Your cancer seems to have become resistant to the chemotherapy you have been having. This can happen to some people, unfortunately. Cancers develop from normal cells that have changed or mutated to become cancerous. The mutation happens in the genes of the cell. These changes make the cell behave differently to a normal cell. Cancer cells continue to mutate, so that they become more and more abnormal. Sometimes the mutations make the cells resistant to chemotherapy.

Your doctor may want to try some different chemotherapy. But unfortunately, sometimes cancers develop resistance to many chemotherapy drugs at the same time. Doctors call this multidrug resistance. Scientists have found a group of genetic mutations that they think cause this. These mutations mean that the cancer cell can keep the drugs out. The resistant cells have high levels of a substance called p-glycoprotein. P-glycoprotein is a protein found in cell walls. The protein acts as a pump and removes toxins from cells. Cells with high p-glycoprotein levels are very good at keeping chemotherapy drugs out. If there is not enough of a chemotherapy drug inside a cancer cell, the drug cannot kill the cell.

Researchers are looking to find ways of overcoming this resistance, so that they can make chemotherapy treatment more effective for more types of cancer.

We have more information about how cancer develops and about how cancer cells behave.

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Updated: 19 January 2015