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
The most reliable prognostic factor for colorectal cancer is the stage of the tumour at the time of diagnosis. As with most cancers, the lower the stage of colorectal cancer, the better the outcome. Tumours that are only in the lining of the colon or rectum have a more favourable prognosis than those that have grown through the muscle wall or that have spread to other organs.
Lymph node involvement
Lymph node involvement is related to the stage of the tumour and is an important prognostic factor. The fewer lymph nodes that the cancer has spread to, the better the prognosis.
Bowel obstruction or perforation
If the tumour has not blocked the colon or grown through the wall of the colon or rectum (perforation), the prognosis is more favourable.
Blood vessel involvement
If the tumour has not invaded the blood vessels in the area, the prognosis is better than if the cancer has spread to the blood vessels.
Lymphatic vessel involvement
If the tumour has only invaded the lymph nodes, but has not spread to the lymphatic vessels, the prognosis is better than if the tumour had invaded the lymphatic vessels.
Grade
Grade describes the aggressiveness of the tumour. The lower the grade of the tumour, the better the prognosis.
Tumour type
Medullary types of colorectal tumours have a better prognosis than other types, such as signet ring, mucinous, and small cell and high-grade neuroendocrine carcinomas.
Perineural invasion
Tumours that have not invaded nearby nerves are thought to have a better prognosis.
Microsatellite instability (MSI)
Microsatellites are repeating sections of DNA. In MSI, the normal number of repeating sections changes. This happens as a result of mutations to genes that normally repair errors during DNA replication. A high degree of MSI (MSI-H) carries a more favourable prognosis.
DNA content
Tumour cells that have a normal number of chromosomes (diploid) have a better prognosis than those that have an abnormal number (aneuploid).
Partial loss of chromosome 18 occurs in approximately half the cases of colorectal cancer. People who have not lost part of chromosome 18 have a better prognosis than those who have partial loss of this chromosome.
Carcinoembryonic antigen (CEA)
CEA is a tumour marker that leaks out of cancer cells and can be measured in the blood. There is still some debate about the reliability of this marker, but it is thought that the lower the CEA level before surgery, the better the prognosis.
Surgical margins
When a colorectal tumour is removed, the surgeon will also take a margin of healthy tissue around the tumour. Margins that are clear of cancer cells suggest a better prognosis than margins that have cancer cells in them.
Inflammatory response to the tumour
Presence of inflammation around the tumour indicates that the body is trying to fight the tumour and may indicate a slightly better prognosis.
Performance status
People with a high performance status (Karnofsky score of 70 or greater) have a more favourable prognosis than those with a lower performance status.