Prognosis and survival for colorectal cancer
People with colorectal cancer may have questions about their prognosis and survival. Prognosis and survival depend on many factors. Only a doctor familiar with a person’s medical history, type of cancer, stage, characteristics of the cancer, treatments chosen and response to treatment can put all of this information together with survival statistics to arrive at a prognosis.
A prognosis is the doctor’s best estimate of how cancer will affect a person and how it will respond to treatment. 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, and 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 more favourable prognosis than those that have grown through the wall of the colon or rectum, or spread to other organs (called distant metastases).
To accurately stage colorectal cancer, doctors need to remove at least 12 lymph nodes during surgery. The lymph nodes that are removed are examined to see if they contain cancer. If not enough lymph nodes are removed and tested, the cancer may be given a lower stage than it truly has. This can mean that not enough treatment is given after surgery so there is a less favourable prognosis.
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 in lymph and blood vessels
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) levels
The lower the CEACEAA protein that is normally found in small amounts in the blood of most healthy people but that can be higher in people who smoke tobacco or have certain types of cancer, particularly colorectal cancer. level before surgery, the more favourable the prognosis.
Bowel obstruction or perforation
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 diagnosis have a less favourable 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.
Type of tumour
Mucinous adenocarcinoma, signet ring cell carcinoma and small cell carcinoma have a less favourable prognosis than other types of colorectal tumours.
Microsatellite instability (MSI)
MSI is a change to the genetic material, or DNA, in a cell. Some colorectal cancer cells show MSI. Tumours that have cells with high MSI (MSI-H) have a more favourable prognosis than tumours without MSI (called microsatellite stable or MSS).
The following genes are linked with colorectal cancer and affect prognosis.
DCC gene is found at chromosomechromosomeThe part of a cell that contains DNA (genetic information). 18q. It is a tumour suppressor gene that normally controls cell growth and death. Part of chromosome 18q, along with the DCC gene, are often missing in colorectal cancer cells. When the DCC gene is missing, cell growth, division and death may be uncontrolled. Missing the DCC gene is also linked with metastases and resistance to chemotherapy. Colorectal tumours with cancer cells that are missing part of chromosome 18q and the DCC gene may have a poor prognosis.
KRAS gene can be mutated, or changed, in some colorectal cancer cells. KRAS gene mutations mean that the cancer cells are unlikely to respond to targeted therapy drugs such as cetuximab (Erbitux) and panitumumab (Vectibix). People with colorectal cancer cells that test positive for the KRAS gene mutation have a less favourable 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 worse prognosis.