Many people turn to the Internet to find out about health issues, such as early detection and prevention of cancer.

Many, including those under 40, then go to their general practitioners and ask for tumour marker screening blood tests, especially if these are paid for by their insurance companies.

I have had patients who, after doing such tests, had sleepless nights and were stressed, and consulted me to interpret their results when the tests showed only a slight increase from the top normal range for the tests.

I had to reassure them, and in some cases do costly tests to detect the source of the markers and see whether the cancer existed in the first place.

Blood cancer markers generally are not specific and not sensitive enough to detect and diagnose cancers, meaning these cancer markers lack specificity and sensitivity to diagnose a specific cancer.

So I generally discourage my patients from doing such screenings, as they are not justified and can cause more worry and unnecessary stress.

Unfortunately many laboratories package cancer marker screening into health screenings.

When my patients insist on cancer marker screenings, I warn them of the lack of sensitivity and specificity so that they will not be overly alarmed when the results are slightly higher than normal.

To be fair, if there is a family history of a certain cancer, patients should consult their family physician who will certainly advise them on what types of screening tests are useful to diagnose early cancer or to exclude it.

For example, it is advisable for women above 40 to do mammograms to detect breast cancer and regular pap smears to detect cervical cancer.

Colonoscopy and gastroscopy are also advisable if there is a family history of colon or gastric cancer, and these are best done 10 years earlier than the age the family member contracted the cancer at, as it generally takes 10 years for a benign polyp to develop into cancer.

Screenings for cancer markers for throat cancer and prostate cancer are also generally sensitive and specific enough to warrant doing them.

Therefore, do trust and see your family physician, who knows you and your lifestyle best and has your records as well as your family's records, to advise you on what kind of cancer screening is necessary at what age. A specialist can also give specific and good medical advice on what is necessary to do.

Screening for cancer markers is also useful when ordered by the oncologist after the patient's cancer has been treated by surgery, chemotherapy or radiotherapy, to monitor progress after the initial treatment and to indicate the prognosis of the patient's cancer.

Andrew Lim Hock Beng (Dr)