Grouping tumors according to the developmental stage their gene activity most resembles reveals predictive information about those tumors, Kohane found. In groups of lung tumors, for instance, “malignancy and even time to death of actual patients were directly proportional to the ‘earliness’ of the gene signatures.”

One reason cancer is not considered a single disease but many is that every cancer cell seems to be dysfunctional in its own way. Random mutations in a cell’s DNA initiate its slide into abnormal behavior. And as additional mutations accumulate, that randomness is also thought to account for the diversity in different patients’ tumors, even when they are cancers of the same tissue. But evidence is growing that there is a method to the madness of tumor cells, making some scientists reevaluate the nature of cancer.

Analyzing tumors from dozens of tissue types, Isaac S. Kohane of the Harvard-MIT Division of Health Sciences and Technology has catalogued surprising yet familiar patterns of gene activity in cancer cells–they are the same programmed genetic instructions active during various stages of embryonic and fetal development. Entire suites of genes that drive an embryo’s early growth and the later formation of limbs and other structures in the womb normally go silent during the rest of life, but these genetic programs are switched back on in many tumor cells.


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