Today thumbnail-size silicon chips called microarrays allow researchers to analyze rapidly and simultaneously the activity of thousands of genes in a cell or tissue all at once. Using microarrays, scientists can count which genes are on and off and how much each gene is "working" in a small sample of normal or tumor tissue. Soon these chips will be routine devices in many diagnostic laboratories, offering genetic fingerprints of patients' tumors. With these data, oncologists may well be able to create custom cancer treatments.
For now, scientists will need to learn more more about the intricate molecular pathways of cancer¿and transgenic mice will be their best allies in the quest.