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C ANCER DIAGNOSIS
W hy Don’t We Sca n a nd Test Ever yone to Detect Ca ncer? Photo: Wellcome Images
by Dr. Chang Yang Yew
I
t is well known that the survival rate of cancer patients is much higher if the cancer is diagnosed at an early stage. As medical technology evolves, there are now an abundance of scans and blood tests available to help doctors detect cancers and other diseases. Putting these two facts together, a natural question is: “Why don’t we scan and test everyone regularly so that we could pick up and cure more cancers?” To answer the question above, it helps to first establish some yardsticks of how we measure the usefulness of a medical test: A test needs to reliably display positive result when a disease
S c i e n t i F i c m a l aY S i a n
is present (in medical jargon it needs to be sensitive) - just imagine the futility of a “cancer test” which misses half of the cancer patients. A test should be reasonably specific, which means that amongst healthy people, it should not give a falsely positive result. False positive results contribute to anxiety and complications from subsequent invasive medical t e s t s a n d p r o c e d u re s . Lastly, the most meaningful measure of a test’s usefulness is its effect on mortality. The important question is, “Does this test save lives?”
It is clear that ideal tests should be 100% sensitive (all cancer patients are detected) and 100% specific (all healthy individuals are negative for cancer). However, due to limitations of many tests, testing everyone indiscriminately is a futile exercise for most diseases. One of the biggest cancer news which hit the mainstream media in recent time was about Jack Andraka, a 15-year-old boy from US who invented a test to detect pancreatic cancer in its early stages, promising a dramatically improved cure rate [1]. Pancreatic cancer is one of the most fatal cancers in the modern era. As the pancreas is seated deep inside
