Cancer incidence rises to become the 2nd most common cause of death

Cancer is the second most common cause of death after cardiovascular disease and will increase in incidence with increased longevity. Thus, many countries have seen a steady annual increase. Approximately three-quarters of all those who die from cancer are 65 or older. Exceptions include testicular cancer, breast cancer and the childhood cancers (leukaemia, lymphoma, brain tumours and Wilm's tumour).

Markers, which indicate that a malignant process is present, are known as tumour markers. They are frequently present due to alterations in the metabolism of cancerous cells and may be found in body fluid such as serum or in the tumour tissue. Obviously, serum based tumour markers are more readily accessible due to the less invasive methods necessary to obtain them. Tumour markers may be directly attributable to tumours, for example, metabolic products, acute-phase proteins, enzymes, tumour-associated reaction products, hormones (hCG) and tumour-associated antigens. The latter includes the oncofoetal antigens such as Carcino-Embryonic Antigen (CEA) and a-Feto Protein (AFP) and those known as hybridoma-defined tumour antigens (CA 125, CA 19.9, CA 15.3, and so forth). Monoclonal antibodies, found in the cell membranes of tumour cells, act against antigens such as glycolipids. They can be located in serum using hybridoma technology. Such technology has subsequently led to the production of several new specific tumour markers.

The following characteristics are required for the ideal tumour marker:

• 100% organ specificity
• 100% accuracy in differentiating between healthy individuals and those with a particular malignant tumour
• The ability to detect all patients with a particular malignancy, and if possible, at a very early stage in the transformation process.
• Excellent correlation between the concentration of the marker and the individual tumour stages including relapse and remission
• Prognostic value of the tumour marker concentration

The first 3 requirements are necessary for use as a screening tool. However, no such tumour marker yet fulfils these criteria. Prostatic Specific Antigen comes closest of all the tumour markers and is widely used in the USA to screen for prostatic carcinoma. Other tumour markers are used for the purpose of monitoring high-risk individuals, for example, AFP in those with liver cirrhosis and hepatitis B.

Tumour markers are very useful for monitoring the course of a diagnosed malignant tumour, for example, pre-treatment and subsequent serial values are essential for the evaluation of the response to the treatment modality with time. Depending on the malignancy, different tumour markers may be expressed and those elevated at the time of diagnosis are the ones that are usually employed for monitoring. Frequently, serum tumour markers are more sensitive than clinical indicators and can direct subsequent investigation and treatment. On occasion, the rate of increase in a tumour marker can be of value, for example, a steep increase in CEA levels is often associated with liver or bone metastases whilst a shallow increase is associated with a local relapse or metastasis in the peritoneal cavity or a soft tissue.