A Brief Overview of Current Methods for Colon Cancer Screening

The incidence of tumours affecting the gastrointestinal system, particularly in the large bowel or colorectal region, has increased considerably in the past few decades. After the prostate and lungs in the case of men, and the breasts and lungs in women, the bowel has become the third most common site of malignancy in both sexes.  The growing incidence has prompted the need to develop reliable test procedures with which to establish the presence or absence of the abnormal cellular activity associated with this condition.

Early diagnosis substantially improves the chances of a successful treatment, and as a consequence, most countries, including South Africa, now routinely provide a number of screening procedures for the detection of colon cancer and other malignancies for those who are considered to be statistically most at risk. These include people with a family history of the disease, the elderly, and those suffering from inflammatory conditions of the bowel, such as Crohn’s disease and ulcerative colitis. In addition, obesity, excessive use of alcohol or tobacco, and eating habits have all been associated with increased risk.

When it is required to screen large numbers of patients, it is important that the tests used should provide doctors with a reliable result as quickly as possible. To achieve this, procedures that once needed to be conducted in a laboratory have had to be modified for rapid use. A classic example of such a test is the faecal occult blood test (FOBT). Once, this would have involved boiling a stool sample in a test tube with benzidine, glacial acetic acid and hydrogen peroxide, to detect the iron present in haemoglobin using the so-called Prussian blue reaction. Today, a more specific FOB test can be performed in a doctor’s surgery. Using paper strips impregnated with guaiac to detect haem, it offers a rapid and inexpensive option for use as a screening test for colon cancer.

The guaiac test, however, requires the patient to refrain from eating certain foods, such as red meat, which also contains haem, for several days prior to testing. A newer detection method, in which antibodies are specifically employed to detect human haemoglobin, is known as a faecal immunochemical test (FIT) and imposes no such dietary restrictions on the patient.

Even more specific than those methods used to detect the presence of various blood components which, incidentally, is not necessarily an indication of malignancy, are tests designed to detect certain DNA biomarkers. For this purpose, a number of kits are now available that combine the detection of occult blood, using a suitable immunochemical reaction together with nine markers carried by three genes that have been found to occur in colorectal malignancies, as well as in the pre-cancerous growths known as adenomas that will often become malignant over time. Clearly, the ability to identify patients in which there is a proven potential for malignancy which has not yet developed is a huge bonus, and makes this an especially effective test for the screening of colon cancer.

Ultimately, of course, additional investigations, such as a sigmoidoscopy and colonoscopy, or even a CT scan are likely to be performed for confirmation of positive findings, but the use of simple tests available from IEPSA reduces the dependence on such labour-intensive, time-consuming, and more expensive examinations.

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