Why isn't my treatment working?

Your cancer seems to have become resistant to chemotherapy. 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 something called 'p-glycoprotein'. This is a protein found in cell walls. It acts as a pump that removes toxins from the cell. 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 have been working on this problem almost as long as chemotherapy has been used. We need to find a way of overcoming resistance if we are to make chemotherapy treatment more effective for more types of cancer. Cancer Research UK researchers have now developed a way of blocking p-glycoprotein. They are working on a drug called tariquidar (XR9576). They have known this could work in individual cells for some time. It has shown some effectiveness when given to patients as part of phase 2 trials but it caused a lot of side effects. Further, bigger trials are being carried out to try to find out exactly how effective it is and reduce the side effects.

There is more about how cancer develops, and about how cancer cells behave in the About Cancer section of CancerHelp UK.