Health August 2013

Is There a Blood Test for Cancer?

No—but age- and gender-related routine tests are advised

Patients often ask me if there is a simple blood test they can undergo to check whether they have cancer.

At some time, most of us will have a close friend or relative with cancer. It is often this close-to-home encounter that prompts patients to ask the above question.

Unfortunately, the answer is “no”. With the exception of blood cancers, even if all routine blood tests are normal, one cannot completely rule out an underlying cancer.

Sometimes, tumour marker blood tests are used. The tests detect chemicals in the blood that are produced by cancerous cells. Well-known tumour markers include prostate specific antigen (PSA) for prostate cancer and CA125 for ovarian cancer.

The problem with using tumour markers is that most of them are produced both by cancerous cells and some normal cells.

Thus, elevated levels of the markers can be found in healthy individuals, while some people with cancer may never present high levels of a tumour marker.

So how are tumour markers used? Below are three main areas of use.

To screen symptom-free people to detect cancer at an early stage, when it is easy to treat.
However, the non-specific nature of the markers makes them of limited use in these tests.

The PSA is the most widely known tumour marker that is used as a screening test in some countries. But, with correct results not guaranteed, whether to conduct a test should depend on each individual’s situation.

Some people who are at particularly high risk of developing certain cancers (for example, due to family history or the presence of underlying disease) may benefit from screening with certain other markers.

To help diagnose symptoms in someone who is unwell by measuring the level of a tumour marker.
The level of the marker is considered, with the patient’s symptoms, imaging and lab tests, as well as biopsy results.

To assess how well the treatment given to a cancer patient is working, and if their cancer has returned.
As a patient responds to treatment, the amount of a tumour marker in the body should fall and possibly normalise. A subsequent rise in the level may indicate that the cancer has recurred. This is currently the most common use of tumour markers.

In Japan, a wide variety of tumour markers are used as screening tests. They are added to routine blood tests performed at annual physical examinations.

However, since tumour markers do not provide accurate screening results, findings need to be interpreted with caution. Preferably, such tests should be avoided in the first place.

Often, one of the tests will come back showing an elevated level of a tumour marker in someone who is completely fit and well. Inevitably, numerous additional tests and scans follow that reveal no underlying cancer—while having caused the patient great anxiety.

Bear this in mind before you tick the “tumour marker” option ahead of your next physical. Otherwise, be ready to deal with the uncertainty of an elevated result.

The best advice we can give our patients regarding cancer testing is that they undergo all the routine tests recommended for their age and gender.

Cervical cancer screening is performed in the UK for women between the ages of 25 and 65. Depending on a woman’s age, screening is done every 3–5 years. Age ranges vary slightly from country to country.

In the UK, breast cancer screening is undertaken every three years for individuals aged from 47 to 73 years. Both men and women, between the ages of 60 and 69, are currently offered bowel cancer screening every two years.

It is also worth remembering that lifestyle factors can influence one’s risk of developing cancer. For example, obesity and smoking increase the risk of bowel cancer; obesity increases the risk of breast cancer in post-menopausal women.

Thus, smoking cessation and maintenance of a healthy body weight are also important.

Finally, there is a lot of research being done to find a blood test that will detect various types of cancer at an early stage. The hope is that, in reply to the question, “Is there a blood test for cancer?”, the answer will one day be a resounding “yes”.