Biomarker testing and mutation prevalence in metastatic colorectal cancer patients in five European countries using a large oncology database.

Lay abstract Each patient's cancer is unique. To find the best medicine for each patient, doctors perform tests to look at the cancer's genes. It is unknown how often and how well these tests are done. We tried to find this out for patients with cancer of the bowel or rectum that has spread to other organs. We found that an important genetic test called RAS is done in most patients. Other tests, called BRAF and microsatellite instability, are also conducted increasingly frequently. This is important because the results of such tests allow doctors to decide which drug(s) should be the most effective depending on the patient's cancer genes.