Question: Does chemotherapy always work? If not is this down to the bodies resistance?

Alexis Barr answered on 18 Jun 2013:

Some chemotherapy works very well – for example there is a drug called Gleevec that is very successful in treating some leukaemias.
The problem with a lot of current chemotherapies is that as well as killing the replicating cancer cells they also kill healthy cells that are replicating – like stem cells in your skin and in your blood. This is why people can get sick from immunosuppression (the immune system is reduced so people can get infections) and might also lose their hair (when stem cells in the skin are killed).
Another reason chemotherapy might not work is because the drug is cleared too quickly out of the body. We try to design drugs so that they stay in the body for longer and so have a better chance of killing cancer cells.
Cancer cells themselves can also become resistant to drugs. Cancer cells often have a high rate of mutation in their DNA. This means that they can mutate genes that the drugs might be targeting so that the drug can no longer kill that cancer cell. Cancer cell resistance to drugs is a big problem and is a reason why some people’s cancers come back after a few years. We are trying to solve this by using multiple drugs to treat cancers as it is unlikely a cancer cell would become resistant to lots of different drugs.