Chemoresistance is a trait found in some cancers, in which they have low sensitivity to chemotherapy drugs and might not respond to these drug therapies. It is closely related to the concept of chemosensitivity, and the same kinds of tests can be used to assess for both. When a patient is diagnosed with cancer, part of the process of developing a treatment plan might involve a test to see which medications would be the most effective. With some cancers, there is an increased risk of chemoresistance, and the doctor wants to avoid prescribing a medication that will not work.
The mechanics behind chemoresistance can be complex. Cancers are very diverse and can arise in many ways within the body. Chemotherapy agents might attempt to kill cancer cells, stop them from proliferating or intervene at some other stage of the process, such as tagging cells for the immune system to destroy. If the cells lack the receptors to match the drug, the chemotherapy medication will not be effective.
Some chemoresistance appears to be genetic in nature. Cancers that have a hereditary link are more likely to also come with hereditary chemoresistance, because the genes are passed down together. Other cancers might have varying degrees of sensitivity. If the patient is given the wrong medication, the cancer might continue to grow and thrive in the body for several weeks before the doctor identifies the problem and switches drugs. This can decrease the chance of a positive outcome.
In a chemoresistance assay, a pathologist can take a small section of the tumor and grow the cells in culture. Next, he or she can add several chemotherapy drugs to different areas of the culture or divide the cells into containers and test each one separately. If the cells continue to grow with a drug present, they are resistant to it. If their growth is slowed or stops, the cancer is chemosensitive for that drug, and that drug can be a good choice for therapy.
Customizing chemotherapy regimens to the needs of the patient and the known traits of the cancer can be important. Patients tend to have a better outcome with targeted therapies, particularly in the case of cancers that have chemoresistance. If the doctor can find a medication that works particularly well on cells in culture, that performance hopefully will repeat inside the patient and eradicate the cancer or radically slow its growth. This can give the patient more time or a chance at treatments such as surgery after the tumor shrinks.