Many different body fluids or tissues can be used during genetic testing, including blood, skin, urine, semen, bone or other tissues. All types of genetic testing must be ordered by a physician and the tests may be completed in a number of locations, such as a commercial laboratory or hospital. Genetic testing involves one or more of the following methods:

• DNA (deoxyribonucleic acid) testing. The sample is analyzed in a laboratory using molecular probes that examine the length of individual DNA molecules and check for a specific coding sequence. Usually, the technician will look for sequences associated with cancer or other serious diseases. DNA testing may focus on a specific gene mutation, a panel of mutations or the complete gene sequence.
  
  
• Cytogenic testing. Analyzes chromosomes for proper structure and arrangement, as well as any abnormalities.
  
  
• Biochemical testing. Examines whether any proteins or enzymes produced by cells are missing. Special preparations, such as fasting or not eating certain foods, may be required before testing.

Genetic testing is available for gene mutations associated with a number of cancers. The most commonly used genetic tests are conducted for:

• Breast cancer. Variations of several genes increase the risk of developing breast cancer. BRCA1 and BRCA2 genes are the primary genes related to hereditary breast cancer and ovarian cancer. If an individual tests positive for an altered BRCA1/2 gene, it is called a "known mutation."  The person has inherited a BRCA mutation and has an increased risk of developing breast and ovarian cancer. In addition, the person has a chance of passing the alteration on to their children.
  
  There are inherited changes in several other genes that have been associated with increased breast cancer risk. These include CHEK2, ATM, BRIP1 and RAD51.  Some studies have also found certain mutations of the AR gene may raise the risk of breast cancer while other research has not shown this connection. Some mutations, known as somatic mutations, are not inherited but acquired during a person's lifetime. Somatic mutations associated with breast cancer include TP53, DIRAS3 and ERBB2 (also known as Her-2/neu). Genetic tests can identify these mutations and help with prediction of cancer as well as prevention options and treatment planning.
  
  In February 2007, the U.S. Food and Drug Administration (FDA) approved of a new genetic test for breast cancer. The test, called MammaPrint, can help determine the likelihood that early stage breast cancer will return within five to 10 years after treatment. It measures the activity of 70 genes from breast cancer tissue, which can provide information about the risk of cancer spreading to another site. The test can help physicians decide whether a breast cancer patient should receive chemotherapy as part of treatment for early stage disease.
  
  Many gene tests for breast cancer are being evaluated in research studies and clinical trials. Researchers have developed two genomic tests to help better predict how patients will respond to hormone therapy or chemotherapy. One test uses a genomic indicator to predict the 10-year survival rate for patients who receive postoperative hormonal therapy with the drug tamoxifen. The second test analyzes 780 different gene combinations to predict a breast cancer patient's response to chemotherapy.
  
  
• Ovarian cancer. Physical examinations and screening tests are not effective in detecting ovarian cancer in the early stages. For that reason, researchers have focused on developing genetic tests to help predict and identify the disease. The tests examine genes, gene expression levels, proteins and tumor markers. As with breast cancer, BRCA1 and BRCA2 mutations have been associated with an increased risk of ovarian cancer. In addition, elevated levels of the tumor marker CA-125 have been linked to ovarian cancer. Other genes are being analyzed for their association to ovarian cancer in research studies and clinical trials.
  
  
• Colon cancer. Inherited forms of colon cancer account for only about 5 percent of these cancers. However, individuals who have a close relative with colon cancer have twice the risk of developing the disease. Genetic testing may be considered by high risk individuals to identify genetic syndromes associated with the colon cancer. Gene mutations are responsible for family adenomatous polyposis (FAP) and Lynch Syndrome, conditions closely associated with colon cancer.
  
  
• Lung cancer. Researchers are studying several genetic tests that may help predict the development of lung cancer, the effectiveness of certain treatments and methods to prevent the disease. Scientists have found that the activity level of two genes, called RRM1 and ERCC1, can help predict the benefit of chemotherapy in lung cancer patients. High activity suggests that a lung cancer patient would do better without post-operative chemotherapy while low activity showed a need for chemo treatment. Other studies have focused on smoker's genes and their ability to repair DNA.