The most exciting breakthroughs these days in cancer treatment are the identification of drugs that target specific genes and proteins. But how do you know if your cancer has the right gene? Does it have the right mutation, expression, or translocation? What tests needs to be ordered? Why can’t they just do a blood test? What are those buzz words like “cancer genomics,” “personalized medicine,” and “molecular profiling” supposed to mean?

The more we understand about cancer biology, the more confusing the nomenclature gets. I’d say that even for oncologists, many, or most, don’t understand the differences between gene expression, protein expression, gene mutations, translocations, and amplification. Although understanding these distinctions isn’t usually necessary to choose the right treatment, for those trying to keep track of the latest research and eligibility for new drugs and clinical trials, it helps to know what is being tested.

On the most basic level, cancer is a disease of the genes. This doesn’t usually mean there is a problem with the genes you were born with, but that as your healthy cells multiply, grow, and die, the genes (DNA) develop errors. When enough of these errors accumulate, the cells develop the ability to keep dividing, multiply quickly, avoid dying, and spread to other places in the body.

Traditional “cytotoxic” (i.e. “cell killing”) chemotherapy poisons cells that are multiplying. Cancer cells, by definition, are multiplying, so they are affected, but so are healthy, dividing cells. Newer “targeted” therapies inhibit the function of one particular gene or protein, which gets back to the original question. What tests determine if your cancer has the right target?

It’s important to understand the basic language and manufacturing process in the cell. DNA is the instruction book, which is screwed up in the cancer cells. DNA is transcribed or “expressed” as RNA, which is then translated, or “expressed” as protein. (See how the double meanings are already confusing?!)

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