Why Resistance Develops One of the mysteries of cancer therapy is why some people respond really well to a treatment while others have problems. About 10 years ago, research on drug resistance led to speculation that multiple resistance developed during therapy and that this was responsible for progressive and uncontrollable metastatic disease.
More recent research has begun to explain how cancer cells become resistant to drugs. There is a protein called P-glycoprotein on the surface of a cancer cell. This protein acts like a pump, regulating the passage of drugs into and out of the cancer cell. Tumor cells with larger amounts of P-glycoprotein may not allow any drugs to enter. This, of course, makes chemotherapy ineffective.
There are now ways to measure the amount of this protein, so it can often be predicted whether a cancer will be resistant to chemotherapy. P-glycoprotein genes have also been discovered, which may explain why some cells in a tumor are resistant to drugs while others are not. This in turn may explain why some drugs are not effective when administered even when a drug sensitivity test indicates that the tumor should be sensitive to a certain drug. Researchers are now trying to overcome drug resistance related to P-glycoprotein.
