We are clearly moving away from using chemotherapy to nonspecifically kill cells to developing targeted treatments. Nearly all cells in the human body carry exactly the same set of genes, and many of these genes, so-called housekeeping genes, are turned on in most cells. But skin cells are different than muscle cells because a unique set of skin genes are turned on in skin cells and a unique set of muscle genes are turned on in muscle cells. Genes give cells their unique characteristics, but the genes have to be turned on, or expressed, for the unique characteristics to appear. By identifying the pattern of gene expression for muscle cells, skin cells or any type of cells, including cancers, scientists can create a genetic fingerprint of that cell type.
Genetic fingerprints can uniquely differentiate one cell type from other cell types.
To create these fingerprints, scientists use a device called a gene expression microarray, or, more commonly, a gene chip. The chip is simply a glass slide on which thousands of known gene samples have been printed in tiny spots. Cells to be tested are then manipulated in such a way that genes expressed in the cell will match up with the known gene samples, like two pieces of Velcro attaching to each other. The cellular genes are treated in such a way that they literally light up the gene dots on the chip. The luminescent pattern is then measured with a special type of microscope and the results fed into a computer for analysis.