Once a diagnosis of Colorectal cancer has been made, it is important to stage the cancer. This is especially vital in the treatment of rectal cancers. All colorectal cancers are staged on the TNM system. T stands for tumor, the first location (primary) where the cancer occurs and source of any spread to other locations. N stands for lymph Nodes. Colon and rectal cancers are adenocarcinomas and therefore have a typical pattern of discontinuous spread to lymph nodes first. M stands for metastasis. Technically, the first spread to lymph nodes is also considered metastasis. Since the local lymph nodes are removed at the time of surgery, they are regarded differently than spread to other organs such as the liver, the lungs or the brain. Staging of cancer at the time of diagnosis helps the physicians determine treatment strategy. In the case of rectal cancer, a rectal ultrasound or a pelvic MRI will provide the T and N stages. MRI or CT scan, usually in combination with a PET scan, will be used to provide limited information about the primary tumor and lymph nodes. Their main role is to identify metastatic disease.