Single cancer cells are impossible to detect even under the microscope - both because they are so small and because they look so much like normal cells most of the time. When a dozen congregate in one location like a street gang amid normal citizens you can make a diagnosis but that is contingent on having biopsied precisely in the right spot and putting the tissue under a microscope. Otherwise we must wait until they multiply enough to become a mass of a million or a billion cells - big enough to feel it or see it. That is what it takes for our fingertips to find it or even our most sensitive tests: mammograms, CT scans, MRIs and X-rays to detect it.

Blood tests such as tumor markers are generally far less sensitive with rare exception (PSAs).The most sensitive such tests are less specific (i.e. they might be elevated for other non-cancer reasons). They require repetition for confirmation and a rising trend over months to raise their credibility. We don’t trust any single test but they are useful to put us on the alert or to inspire other forms of testing aimed at unique characteristics of cancer tissue: They are often denser because the cancer cells crowd together. They grow faster than normal cells, albeit still slowly, and accordingly cancer cells consume food (glucose) faster than normal cells. Accordingly their presence can be detected by when they avidly consume specially labeled sugar molecules or radioactively labeled substances needed for growth such as iodine or technetium.

Beware of following the exact value of a tumor marker; they can rise or fall a small amount for multiple reasons unrelated to tumor growth. Your physician will tell you what a significant change is. So don’t waste an ounce of anxiety over anything less. As often as not the tumor marker will bounce down next time you test it. There have been patients who were considering killing themselves over a small rise. One inappropriatelly frightened patient and friend who was mislead by a small insignificant rise of her Ca 125 marker threatened to take her life but lived on for another 10 years to die of natural causes with no evidence of cancer to be found anywhere in her body. Trust your doc on this. Forewarned is forearmed. Tumor Markers are inaccurately named as they measure other things besides cancer.

Because we usually cannot detect cancer masses until they are in groups of a million or more we often either initiate cancer treatment based just on a risk assessment even while all tests are negative or continue treatment even after all tests show disappearance of all the original masses. Such disappearance signifies remission but not cure. Only the failure of a cancer to grow back and become visible over time creates confidence of cure. If a given cancer is one of the faster ones then our confidence of cure comes sooner - perhaps in just 2 yrs where as we must wait 5-10 or maybe 15 yrs to be similarly confident of cure of a slower growing cancers.

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