The table below lists examples of some cancers for which genetic testing may be used to help make decisions about targeted drug therapy.
|Type of Cancer||Gene Tested*||Interpretation of Test Result|
|Breast cancer||Her2/neu||When present, likely response to trastuzumab|
|Chronic myelogenous leukemia (CML)||ABL1||Nonresponsive to imatinib when mutation(s) present|
|BCR-ABL||When present, can be measured periodically to monitor response to targeted drug|
|Colon cancer||KRAS||When mutation present, likely resistance to tyrosine kinase inhibitor|
|BRAF||Poor prognosis when mutation present|
|Gastrointestinal stromal tumor (GIST)—rare tumors of the digestive tract||KIT||Depending on mutation present, better response to imatinib therapy, increased dose of imatinib likely necessary and better response to sunitinib, or possible resistance to imatinib|
|PDGFRA||When mutation present, less likely to respond to imatinib|
|Melanoma||BRAF||Better response to vemurafenib when mutation present with metastatic melanoma|
|Myeloproliferative neoplasms (MPNs)||JAK2||When mutation present, may be measured periodically to monitor responsiveness to treatment (e.g., Ruxolitinib)|
|Non-small cell lung cancer (NSCLC)||EGFR||Best response to tyrosine kinase inhibitors such as gefitinib and erlotinib in those with certain mutations|
|EML4-ALK||If ALK is present, may respond to ALK kinase inhibitors, such as crizotinib|
|ROS1||If ROS1 is present, ALK kinase inhibitors, such as crizotinib|
|KRAS||Poorer prognosis when certain mutations present, resistance to tyrosine kinase inhibitors, and poor response to platinum/vinorelbine therapy|
|PDL1||Likely response to immunotherapy|
|Cancers of unknown origin—cancers detected in unusual body sites and thought to have spread (metastasized) from another location||Several genes evaluated together (genomic array or profile)||Helps determine the organ or body part in which the cancer originated in order to help guide treatment|
* Gene names are typically abbreviated for ease of use because full names are often several words long. For additional details about these, see Genetics Home Reference: Genes.
Usually, the cancer drugs and genetic tests listed in the table above have been developed concurrently; thus, the tests are referred to as "companion diagnostics." These are laboratory tests that are developed specifically to "provide information that is essential for the safe and effective use of a corresponding therapeutic product," according to the U.S. Food and Drug Administration (FDA). In many cases, results from these tests are needed for healthcare practitioners to be able to make decisions regarding treatment of their patients.
Cancers associated with a strong family history and those that occur at a young age may have different characteristics than those that develop sporadically in adults. For instance, pediatric cases of GIST are very different than adult cases and do not typically have KIT or PDGFRA mutations.
Only common mutations are tested. A negative test result does not rule out the possibility that a person has a less common mutation. To rule out the possibility that the mutation was not present in the sample tested, additional samples may be needed.
Some tests for specific gene mutations in certain types of cancer are available on a limited basis and/or not used routinely for medical purposes. These genetic tests may, however, be used in research settings and their utility in medical care may evolve as research progresses. Some examples include:
- Colon cancer: PIK3CA and NRAS
- Melanoma: KIT and NRAS
- Myeloproliferative neoplasms: PDGFRA