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Just a Blood Test to Find Out If You Have Cancer - Too good to be true?

By Dr Evelyn Ho

“Take this simple test – all you need is just a small sample of blood to find out if you have cancer.”

Oooh… music to all our ears – what a relief! No probing, prodding, and poking around with our bodies, subjecting it to sometimes uncomfortable procedures to detect cancer early. In addition, the cost seems reasonable enough…or so we think!

Wake up! Does the ideal blood/serum tumour marker test exist?

The ideal test is such that the test result is only raised when the specific malignant tumour is present; preferably indicating the part of the body in which it is growing; can be correlated with the size of the tumour; responds rapidly to changes in the tumour size; easy and cheap to measure using laboratory tests.

Unfortunately, no such test satisfies all the above criteria. As for its uses, serum tumour markers have limited value in screening for cancers and diagnosis. Contrary to what everyone believes, the real value of tumour markers are in monitoring your response to treatment and if raised for the particular cancer that you have, then, re-detecting early recurrence after treatment.

So what are serum tumour markers or blood cancer markers?

These are substances in the blood which are related to the presence or progress of a tumour. Please note that a tumour may or may not be dangerous growth (benign vs malignant tumour). Not all malignant tumours are cancers, although in general the word cancer to the “person on the street” means a dangerous, life threatening growth.

There are 4 main groups of tumour markers. Amongst these are secretions or enzymes, cell markers (may be in the genes), molecules found on the cell surface (such as CA 19-9, CA 15-3, CA125) and those which are products of cell turnover.

Are the serum tumour markers reliable?

Unfortunately most of the markers are not reliable for screening and diagnosing malignant tumours. In America, the FDA (Food and Drug Administration) has only approved PSA (prostate specific antigen) for screening for prostate cancer. Even so, for prostate cancer in America, in those screened and with PSA raised above 4ng/ml, the incidence of prostate cancer is only approximately 30%. The justification for the screening PSA test in men over the age of 50 years in America is also because prostate cancer is a leading cancer in men in that country.

The regular inclusion of blood cancer markers in packaged wellness or screening blood tests have misled many to believe that these markers may hold the key to early detection of a variety of cancers. Sadly, the evidence from many scientific studies does not support the use of the serum tumour markers for widespread indiscriminate screening.

Most commonly requested serum tumour markers are produced by many different tissues in the body. In other words, having a raised marker say CA19.9 cannot really tell us which organ in the body the cancer originating in. It could be from a cancer in the pancreas, liver, stomach or large intestine or it could be raised in inflammation of the pancreas, liver cirrhosis and cystic fibrosis.

By the time the tumour markers are markedly raised and therefore more specific – you or most people would have signs and symptoms and imaging tests would be more directed and focused. In many early tumours, the tumour markers may not be raised or detectable. Again, not all tumours express tumour markers.

Pros and Cons of Serum Tumour Markers

Although these blood tests have some value, depending on the situation or as in the case of prostate cancer; many of them result in unnecessary further tests in the search for an elusive sometimes non-existent cancer or malignant tumour.

The anguish and anxiety, not to mention, money and time involved can actually result in immeasurable costs to the person. This translates to increased healthcare costs to the government as well.

For example: The finding of a slightly raised serum carcinoembryonic antigen (CEA), for instance, for which there can be several causes, could lead to investigation of a patient for colorectal carcinoma, involving a colonoscopy, CT abdomen or an MRI abdomen to rule out a malignancy. Besides the expense incurred, undue anxiety is experienced by the patient. CEA is also almost never raised in early cancers or malignant tumours.

What happens if I have a positive tumour marker – but investigations have been negative?

When do I stop having to worry?

How certain can I be?

How will it impact me should I want to buy life or health insurance?

Now these are questions that one must ask oneself before asking for these blood tumour markers when you have no signs or symptoms of any disease.

Depending on the level of the raised marker and the degree of anxiety or concern that you and your doctor have, you would have embarked on a journey of several investigations. If they prove negative, you may continue to do even more tests which have greater sensitivity at a higher cost to you. It is very difficult to remove the nagging doubt at the back of your mind that you may an early cancer that is still so small it is elusive to the armamentarium of imaging and other investigations. Who would dare to tell you that you don’t have any cancer? Especially when we know a negative test itself may not mean you do not have a cancer.

In all probability, you will be asked to repeat the tests to see if it is persistently raised or continues to increase over time.

What happens when you want to buy health or life insurance? Surely these positive tests will impact on your insurability or premiums you have to pay even if some of these tests are non specific. The situation may be akin to genetic testing for some cancers – the insurability of such persons once tested positive is almost next to none – as this is advanced notice of the risk of cancer. In such situations, counseling is mandatory before the tests are done.

So the next time you think you are getting a good package deal for blood tests including cancer markers – consider what you may be getting yourself into! (This applies only to pure screening scenarios – and not the situation where you have signs and symptoms and your doctor may have recommended a specific marker to be done along with other investigations.)

Find out more at:

Clinical Practice Guidelines on Serum Tumour Markers, 2003. Academy of Medicine of Malaysia and Ministry of Health of Malaysia.
www.acadmed.org.my
The Pathology Service of St Vincent’s Hospital, Sydney, Australia. http://www.sydpath.stvincents.com.au/tests/InfSheets.htm

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Last Updated:
Friday, 22 April 2005