The test must be conducted on the tumour tissue. Tumour tissue removed from the body (following biopsy or surgery) is processed into a tissue block and stored at the hospital where the operation takes place. Once a decision is made to test for KRAS mutations, the patient's doctor will arrange to have a portion of that saved tissue block sent to a laboratory where KRAS testing is conducted. Results are then sent back to the treating physician. The testing process may take up to 2-3 weeks.