Virtual Medical Centre

Biomarkers of colorectal cancer

• What are tumour biomarkers?
• How are tumour biomarkers used?
• How and when are they measured?

What are tumour biomarkers?

Tumour biomarkers are chemicals that are made by tumour cells or other cells of our body, in response to cancer or other benign conditions. Different types of cancers or tumours may be associated with different tumour biomarkers. Colorectal cancer (CRC), which includes colon cancer and rectal cancer is responsible for half a million deaths worldwide every year. There are also about one million new cases diagnosed annually, making it the third most common cancer in the world. Early detection, accurate diagnosis and intensive surveillance are important for best improving a patient's prognosis and response to therapy.

There are a number of methods that doctors use to detect CRC including sigmoidoscopy, colonoscopy and barium enema. Some newer techniques being investigated for effective detection and monitoring of CRC are CT colonography and molecular biomarkers. The use of tumour biomarkers gives doctors a non-invasive way of detecting and monitoring CRC.

How are tumour biomarkers used?

Doctors can use tumour biomarkers in the detection, prognosis and management of some types of cancer, including CRC. An abnormal level of tumour biomarker is usually not enough for a complete diagnosis of cancer and is usually combined with other tests such as a biopsy. The type of biomarker detected and its levels can give an indication to what type of cancer may be present, whether or not it is malignant and what the best treatment may be.

Tumour markers are used during the treatment of cancer in order to monitor the effectiveness of a therapy and how the patient may be responding to the treatment. If levels of a tumour biomarker decrease it may mean that the cancer is responding to treatment. If levels remain the same or increase after treatment it may be an indication that the therapy is not working. Continued monitoring of tumour biomarker levels following treatment can be used to check for recurrence of the cancer.

How and when are they measured?

Different tumour biomarkers are measured in different ways and from different sources. Some markers are found in blood or urine, so these would require you provide a small amount of blood or a urine sample. Other tumour biomarkers such as those involved in faecal occult blood testing (FOBT) can be isolated from faecal matter and require a stool sample. Tissue samples can also contain tumour biomarkers and may involve a tissue biopsy. This is a more invasive procedure than urine or stool sampling. After a doctor takes the sample they are sent to a laboratory for testing using various methods to determine biomarker levels. Particular foods such as red meats or fruits and vegetables can influence the assay and cause false positive results.

Two key factors for an effective tumour biomarker assay are:

1. The assay must be sensitive in its ability to accurately detect disease; and
2. The assay must be specific for the particular malignancy.