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Tumour markers

By DR MILTON LUM

December 21, 2005 - It is common to find tests for tumour markers among screening packages from the various hospitals and laboratories. Tumour markers are substances which are found in higher than normal amounts in the blood, urine or tissues of people with certain types of cancer. These markers are produced by the tumour itself or by the body’s response to the tumour, which can be cancerous or non-cancerous (benign). It is important to always bear in mind that most tumours are benign.

Are tumour markers diagnostic of cancer?

When used with other tests, like imaging (e.g. x-rays, ultrasound, pathology etc), markers are used in the detection and diagnosis of cancer. Some markers are useful in helping doctors plan the treatment of cancer. Some markers provide an indication of the extent of the cancer and can be of use in predicting how it will respond to treatment. Some markers are measured to assess the response to treatment. If the level of the markers measured decreases, it is an indication that the cancer is responding to treatment. If the level of the marker increases, it may indicate that the cancer is growing. Markers are also measured after treatment has been completed as part of the checks for any recurrence of the cancer. These checks include physical examination, imaging and, in some instances, procedures.

However, markers, by themselves, are not adequate to make a diagnosis of cancer because:

Markers are increased in people who have non-cancerous (benign) conditions or it can be present at some level in most or all healthy people.

Many, if not most, of the markers are not specific for a particular type of cancer. A particular marker can be increased in more than one type of cancer.

Markers are not increased in every patient with cancer, particularly in the early stages. The person who is in the best position to explain the role of markers in the detection, diagnosis and treatment of cancer is your doctor. Some of the commonly measured tumour markers are:
Human chorionic gonadotrophin

The placenta in a pregnant woman produces human chorionic gonadotrophin (HCG). It is initially produced in small amounts but as pregnancy advances, the amount produced increases. HCG is used as the basis of most pregnancy tests. Women who are not pregnant do not have HCG in their urine or blood. However, the use of marijuana can also lead to increased HCG levels.

HCG is increased markedly in gestational trophoblastic disease (GTD), a group of conditions in which there is abnormal growth of cells in the pregnant uterus. GTD begins in the layer of cells called the trophoblast, which surrounds the embryo.

In most pregnancies, the trophoblast develops into the placenta. However, it sometimes becomes swollen with fluid that grows and forms grape-like structures. A normal baby does not develop when there is GTD, although the term molar pregnancy is used for the benign condition. A molar pregnancy can lead to the cancerous form called choriocarcinoma, which can also occur after a normal pregnancy or a miscarriage. Choriocarcinoma is more likely to spread to organs away from the uterus.

Increased HCG levels are also found in cancers of the ovary, testis, stomach, liver, pancreas and lung.

Alpha fetoprotein

Alpha fetoprotein (AFP) is produced by the developing foetus in a pregnant woman. AFP may increase in benign conditions, like hepatitis and liver cirrhosis. An increase of AFP suggests the presence of primary liver cancer, ovarian cancer or testicular cancer. It is uncommon for AFP to be increased in other cancers.

Carcinoembryonic antigen

Carcinoembryonic antigen (CEA) is found in small amounts in the blood of most healthy people. It may increase in smokers and people who have benign conditions, like liver conditions, inflammatory bowel disease and pancreatitis.

CEA is produced in large amounts in colorectal cancer. Other cancers that can produce increased CEA levels include cancers of the breast, lung, stomach, liver, pancreas, kidney, cervix, ovary and bladder.

By itself, a raised CEA level does not mean that there is colorectal cancer.

CA 125

CA 125 is produced by different kinds of cells, especially in ovarian cancer. CA 125 is also increased in cancers of the uterus, cervix, breast, liver, colon, pancreas and lung.

It is increased, too, in benign conditions like menstruation, pregnancy, endometriosis, pelvic inflammatory disease, liver disease, peritonitis (inflammation of the lining of the abdominal cavity) and pleuritis (inflammation of the pleura, the tissue lining of the lungs and the chest cavity).

Prostate specific antigen

Prostate specific antigen (PSA) is present in small amounts in the blood of all adult males. It is produced by both normal and abnormal cells of the prostate gland. Increased PSA levels are found in benign conditions, like inflammation of the prostate (prostatitis) and benign prostatic hyperplasia (BPH), which is present in most males above 50 years of age.

PSA is also increased in males with cancer of the prostate. But other tests are needed to check if there is cancer.

CA 19-9

CA 19-9 is not used for screening colorectal cancer because of the high false positive rates, i.e. positive results in patients who do not have the cancer.

CA 19-9 levels are also increased in benign conditions like gallstones, cholecystitis, liver cirrhosis and pancreatitis.

CA 15-3

CA 15-3 is a substance that is increased in breast cancer, particularly in the advanced stage. It is seldom increased in the early stages of breast cancer. CA 15-3 may increase in cancers of the ovary, prostate and lung. It is also increased in benign conditions, like pregnancy, lactation, benign breast or ovarian conditions, endometriosis, pelvic inflammatory disease and hepatitis.

Dr Milton Lum is Chairperson of the Commonwealth Medical Trust. This article provides general information only and is not intended to replace, dictate or define evaluation by a qualified doctor. The views expressed do not represent that of any organisation that the writer is associated with.