Cancer Screening – What You Need to Know Before You Start

Screening aims to reduce your chances of dying of cancer. However, it is impossible to screen for all possible sites of the disease. Today we have the means to look inside the human body entirely. We even have the means to look for the biological activity of cancer cells which is by itself like a fourth dimension in cancer diagnosis. This technology is known as Positron Emission Tomography (PET) and it involves using radioactive molecules which are metabolized by cancer cells differently compared to normal cells. When combined with Computerized Tomography (CT) scanning, the end result is as close to a whole body scan for finding cancer as can be. Unfortunately the technology is not yet perfect in that there is a risk of identifying lesions which mimic cancer but really are not. This may lead to unnecessary invasive procedures to clarify matters. Furthermore, the radioisotopes used in this procedure are prohibitively expensive. It is therefore unlikely that PET scans can be used for routine cancer screening at this time.

Screening for cancer needs to be individualized. A systematic effort to identify your risk of developing cancer, with specific tests focused on these risks will achieve the desired effect, which either an early diagnosis and hence, a better chance of cure or, quite simply, peace of mind.

For example, A 50 year old lady who smokes 1 packet of cigarettes a day for the last 20 years. She has a sibling who had breast cancer which was diagnosed at the age of 34. She is otherwise well. Her preliminary blood tests detected a blood hemoglobin level of 10.5 g%. No other abnormalities were detected.

This patient’s present clinical condition and living environment puts her at risk for a number of common cancers. She is at risk of developing lung cancer, breast cancer and there is a chance that she may already have colonic cancer. It would be wise if she underwent a low dose CT Chest, Mammography and had a stool test for occult bleeding. These tests have a very high chance of detecting cancer (a positive stool for occult blood will require a colonoscopy to detect the underlying colorectal cancer). Similar tests done yearly will decrease her chances of dying from cancer related illness. This is not to say that these tests are completely foolproof as there is a small chance one can be affected in between testing or tests may be incorrectly interpreted, one may also be inflicted by a kind of cancer that these tests are not designed to diagnose. However, the chances of missing a cancer with these tests are much less than they would be with other kinds of tests. This is described as these tests having a high sensitivity for the kind of cancer tested for. With a regular follow up, it is likely that early symptoms of any cancer will be recognized sooner.

Some tests used for screening have risks of their own. For example, use of CT scans for screening comes with a small risk of developing cancer on account of radiation exposure. With modern multi-slice scanners this risk is decreasing. However, each of us will have to be convinced of the benefit of these tests in the long run as these are stacked against such risks.

Risk reduction advice for our patient would start with advice on the various methods available to assist one to stop smoking. This can include behavioral changes and nicotine replacement. Detailed genetic counselling and testing for mutations that are known to be associated with cancer is another option that can discussed. These tests are available but require professional interpretation. Our patient should be advised to keep her weight in a healthy range and would do well to take a diet rich in vegetables and fruits while avoiding red meats.

In another example, Mr. Y is a 42 year old man with no certain evidence of cancer in the family. However he suspects 2 of his elder brothers had bowel cancer as they had passed away due to abdominal symptoms before 40. Mr. Y has a good appetite and is overweight.

International guidelines are clear that if there is a history of colorectal cancer in one’s immediate family, then you are at increased risk for the disease. However, in Mr. Y’s case a doctor will have decide on the likelihood of his suspicion. If it seems very likely, then Mr. Y should undergo colonoscopy – an invasive procedure whereby a fiber-optic endoscope is passed along the length of the colon through the anus. This procedure will detect and can confirm any cancerous or ‘precancerous’ tumors in the colon with certainty. Another option could be a less invasive fecal occult blood test and sigmoidoscopy which may be the right option if the family history is in doubt.