Is there ‘Super Test’ for Cancer? How about a PET scan ?

Madhuri’s mother was diagnosed with Colon cancer when she started passing blood in the stool and her hemoglobin fell to 8 gms. She then underwent investigations and was diagnosed; following which she came to me for surgery. Obviously there was immense panic in the family. Immediately Madhuri, her brother and sister asked me frantically if there is a ‘super test’ for cancer. A single test to say whether cancer is present or NOT. Then the whole family can get the test done !

There has always been a demand from the public, along with determined efforts from the research community to find a single blood test that can identify cancer. In the last couple of decades, there have been many false starts and false hopes;

The first set of blood-tests were called ‘tumour markers’, which are proteins circulated from the tumour cells. CEA was one such marker which was identified in colon cancer patients. The immediate expectation was “Oh! Yes” there is a blood test that can identify colon cancer. However, as people started getting checked for CEA it was found that CEA was not only high in colon cancer but also in colitis, in smokers and in many other non-malignant situations including cirrhosis of the liver.

This is the fundamental truth about cancer. As the cancer cell is very similar to normal cells, the protein secreted or discharged from cancer cells are also similar to those from the normal cells. Most of the screening tests lack the specificity expected out of such investigation.

The second important push for cancer diagnosis has been ‘imaging’, for example; Abdominal CT scans. Its an important investigation to detect a tumour, but is not recommended as a routine test just to reduce your anxiety.

The most frequently ill-advised investigation is the PET Scan. Unfortunately it’s being prescribed by family physicians – “When anyone is anxious about a cancer, Get a PET scan done “. Recently we went to a shop and the owner came to know that I am an oncosurgeon. His first question was, “How frequently should I get a PET scan done?”.

A PET Scan is based on the principle that the tumour cells uptake and metabolize glucose of the normal cell. But again there are many fallacies; (1) it should only be used for staging for cancer and not screening normal population (2) it should never be used to satisfy anxiety of relative diagnosed with cancer. There are many false positives like a simple infection can lead to increased glucose uptake of cells and show positive on PET Scan.

Recently a patient came and said “My brain is affected”. I asked ‘Why”? he said “It shows in the PET Scan”.   Obviously it will be shown because brain is one of the most metabolically active organ. Any investigation needs to be done after careful thought and then also interpreted in the context of ordering and not randomly.

In short, there is no single test that can be used in the community to detect cancer. Once again I go back to the same advice – Be aware of the symptoms and then get appropriate investigations. ‘Seven warning signals’ , Caution and Action ( see earlier blog) are the best bet we have for early detection.

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