How genes can help in the diagnosis and treatment of cancer
We have already talked about ways genes, gene mutations, and gene variations can affect cancer risk and even lead to cancer. In this section, we are going to talk about how finding certain genes or gene mutations can be helpful in diagnosing cancer, monitoring the effects of treatment, learning about prognosis (outlook), and in treating cancer. In each case, only one or two examples are given. To learn about how genes are important to other kinds of cancer, see our document about that kind of cancer.
Cancer diagnosis and monitoring treatment
Certain mutations are commonly found in the cells of some types of cancers. Finding certain mutations in cells can confirm the diagnosis of that cancer. Testing cells for the mutation can also be used after diagnosis to see how the cancer is responding to treatment.
For example, the leukemia cells of patients with chronic myeloid leukemia (CML) contain a mutated gene called BCR-ABL. In order to be diagnosed with CML, this mutation must be present, so testing for this mutation is used to confirm the diagnosis. Very sensitive tests can tell how many copies of this mutation are present in a blood sample (which indicates how many CML cells are present). These tests can find even tiny amounts, representing small numbers of CML cells among millions of normal cells. The number of copies is determined when treatment is started, and then again sometime later to see how well the treatment is working. If treatment has put the leukemia into remission, this test can be used to see if it is coming back and new treatment is needed.
Genes and cancer prognosis
In some cancers, specific gene changes can be used to predict which patients are likely to have a better or worse outcome. This can help guide the intensity of treatment.
For example, patients with acute myeloid leukemia (AML) whose leukemia cells have a mutation in the FLT3 gene have a poorer prognosis than patients whose leukemia cells do not contain that mutation. Doctors may recommend more intense treatment, including stem cell transplant for someone whose leukemia cells have this mutation. On the other hand, people whose leukemia cells have mutations in the NPM1 gene (and no other abnormalities) seem to have a better prognosis than people without this mutation. As a result, doctors may not feel that a stem cell transplant is needed in someone whose leukemia cells only have a NPM1 mutation.
For some cancers, tests that look at the activity (expression) of many genes at once can be useful in predicting prognosis. These tests, called gene expression panels, are performed on samples of the cancer. They are available for a number of cancers, including breast, colon, and prostate cancers. These tests can help predict which patients are more likely to have their cancers come back after treatment. So far, though, only one, the Oncotype Dx® breast cancer assay, has been shown to help predict which patients benefit the most from certain treatments.
Genes and cancer treatment
Drugs targeting genes or gene mutations
Drugs have been developed that target some of the gene changes in certain cancers. Actually these drugs often target the protein made by the abnormal gene (and not the gene itself).
For example, HER2/neu is a proto-oncogene in normal cells that helps them grow. It becomes an oncogene when a cell has too many copies of this gene. When this happens, the cells make too much HER2/neu protein and the cancer is said to be HER2 positive. Patients with breast cancer with cells that are HER2 positive do not respond as well to certain chemotherapy drugs. But newer drugs such as trastuzumab (Herceptin®), lapatinib (Tykerb®), and several others, have been designed to specifically attack cells that are HER2 positive. These drugs can slow cancer cell growth and improve outcomes in patients with HER2 positive cancers. Breast cancers are now routinely tested to see if they are or the HER2 positive to identify which patients will benefit from these drugs. Other cancers also can be HER2 positive. Anti-HER2 therapy has also helped people with stomach cancer that is HER2-positive.
In chronic myeloid leukemia (CML), the cancer cells have a gene change called BCR-ABL that makes a type of protein called a tyrosine kinase. Drugs that target the BCR-ABL protein, such as imatinib (Gleevec®), are often very effective against CML. They lead to remission of the leukemia in most patients treated in the early stages of their disease.
Drugs targeting certain mutations are useful in a number of other cancers including acute lymphocytic leukemia, gastrointestinal stromal tumors, non-small cell lung cancer, a certain kind of non-Hodgkin lymphoma, and melanoma.
Drugs that activate genes
DNA methylation is one way to turn-off genes. Drugs called hypomethylating agents can reverse methylation. This can be helpful in treating some cancers in which some genes are abnormally methylated. For example, in myelodysplastic syndrome, certain genes that are often methylated in the cancer cells when they aren’t supposed to be. The hypomethylating agents decitabine (Dacogen®) and azacytidine (Vidaza®) can decrease this abnormal methylation, which can be useful in treating this disease.
Other drugs that help fight cancer by activating genes are the histone deacetylase inhibitors, such as vorinostat (Zolinza®) and romidepsin (Istodax®).
Gene testing to help predict if a drug will work
Some drugs don’t help patients if the cancer cells have certain gene mutations. For example, cetuximab (Erbitux®) and panitumumab (Vectibix®) are drugs used to treat advanced colorectal cancers. However, these drugs don’t help patients with cancers that have mutations in the KRAS gene, so doctors check the cancer cells for these mutations before they give either of these drugs.
Some drugs work better in people with certain mutations. For example, the drug erlotinib (Tarceva®), which can be used to treat non-small cell lung cancer, works better in patients whose cancer cells have a certain mutation in the EGFR gene.
Many researchers are very hopeful about the future of cancer treatments based on the specific gene changes found in cancer cells, and this remains a very active area of research. There are many clinical trials under way today that could lead to better treatments for many types of cancer.
National Society of Genetic Counselors (NSGC)
Offers a "Consumer Information" link with the following:
- "Making Sense of Your Genes" – a 24-page guide to genetic counseling (may be downloaded and printed)
- Directory of genetic counselors – may be searched by your area
- "Five Questions to Ask Before Considering Genetic Testing" (may be downloaded and printed)
- Guide on collecting family history – a helpful tool in determining possible genetic risks
- FAQs on genetic testing and genetic counselors
Last Medical Review: June 25, 2014 Last Revised: June 25, 2014