Prognosis and survival for colorectal cancer

If you have colorectal cancer, you may have questions about your prognosis. A prognosis is the doctor’s best estimate of how cancer will affect someone and how it will respond to treatment. Prognosis and survival depend on many factors. Only a doctor familiar with your medical history, the type and stage and other features of the cancer, the treatments chosen and the response to treatment can put all of this information together with survival statistics to arrive at a prognosis.

A prognostic factor is an aspect of the cancer or a characteristic of the person that the doctor will consider when making a prognosis. A predictive factor influences how a cancer will respond to a certain treatment. Prognostic and predictive factors are often discussed together. They both play a part in deciding on a treatment plan and a prognosis.

The following are prognostic and predictive factors for colorectal cancer.

Stage is the most important prognostic factor for colorectal cancer. The lower the stage at diagnosis, the better the outcome. Tumours that are only in the colon or rectum have a better prognosis than those that have grown through the wall of the colon or rectum, or have spread to other organs (called distant metastases).

When a colorectal tumour is removed, the surgeon also removes a margin of healthy tissue around it. The prognosis is better if there are no cancer cells in the tissue removed with the tumour than if there are cancer cells in the tissue (called positive surgical margins).

Cancer cells can move or grow into nearby lymph vessels and blood vessels. This is called lymphovascular invasion. Tumours that don’t have lymphovascular invasion have a better prognosis than tumours that have lymphovascular invasion.

Carcinoembryonic antigen (CEA) is a protein normally found in very low levels in the blood of adults. The CEA blood level may be increased in certain types of cancer and non-cancerous (benign) conditions. The lower the CEA level before surgery, the better the prognosis.

A bowel obstruction is a blockage in the intestine. A bowel perforation is a hole or tear in the intestine. People who have a bowel obstruction or perforation at the time of diagnosis have a poorer prognosis.

High-grade colorectal cancer means that the cancer cells are poorly differentiated or undifferentiated. High-grade cancers have a poorer prognosis than low-grade cancers.

Mucinous adenocarcinoma, signet ring cell carcinoma and small cell carcinoma have a poorer prognosis than other types of colorectal tumours.

MSI is a change to the DNA in a cell. Some colorectal cancer cells show MSI. Tumours that have cells with high MSI have a better prognosis than tumours with low MSI (called microsatellite stable or MSS tumours). High MSI is seen in 20% of people with stage 2 disease, 10% of people with stage 3 disease and less than 5% of people with stage 4 disease.

KRAS is a gene that can be changed (mutated) in some colorectal cancer cells. KRAS gene mutations mean that the cancer cells are unlikely to respond to targeted therapy drugs. People with colorectal cancer cells that have the KRAS gene mutation have a poorer prognosis because targeted therapy drugs will not work on the tumour.

BRAF gene mutations mean that the cancer cells may be more aggressive. As a result, people with cancer cells that have the BRAF gene mutation have a poorer prognosis. Less than 10% of all colorectal cancers have the BRAF gene mutation.