The promise and the problems
The idea that specific genes and proteins can be used to diagnose cancer and dictate treatment is an immensely exciting notion to cancer clinicians and researchers. Markers are "the apple pie and motherhood of molecular cancer research," says M. D. Anderson's top pathologist, Stanley Hamilton, M.D., head of the Division of Pathology and Laboratory Medicine. "And perhaps even more than genes, proteins are the ultimate participants in the molecular processes important to cancer."
But even as scientists work long and hard to find the specific genes and proteins that signify, say, prostate cancer that will spread, or breast tumors that will remain benign, they know they have a long row to hoe.
Although the 45,000 or so genes in a human cell have been catalogued, scientists do not know the function of most of the genes. The proteins that genes produce are even more mysterious: researchers estimate that each gene can give instructions for as many as 100 different proteins.
Worse still, investigators are finding that the biology of a cancer cell is changeable, so that genes and proteins found to be switched on in a cancer cell one day may not be active the next day. For example, when a chemotherapy drug shuts down one crucial molecular "pathway" of protein in a tumor, other redundant pathways may take over.
When Hamilton looked at what happened to genes in colon cancer cells after exposure to the common chemotherapy drug 5FU, he saw "an astounding change in gene response 500 genes showed alterations, and 15 percent of all genes in the cell changed their response in a three-day period," he says. "Cancer cells don't sit by and let themselves be killed. They respond with an absolute ballet of protein molecules handing off functions to one another."