Parallel, independent reversions to an embryonic expression phenotype in multiple types of cancer.

Changes in gene expression provide a valuable frame of reference for explaining the development and progression of cancer. Many tissue types radically alter their gene expression profile after becoming oncogenic. We evaluate this change in gene expression in 8 different cancer lines by comparing their expression profiles to that of their associated differentiated tissues as well as profiles for proliferative human embryonic stem cells. We find that, for non-proliferative tissues, the alterations in expression after oncogenesis result in a profile that is significantly more similar to the embryonic expression profile than to the original tissue profile. We also find that the lists of co-similar genes among embryonic and tumor cells are clustered within gene regulatory, protein interaction and metabolic networks. There is however little overlap in these lists between cancer lines and no pattern shared among all cancers in this analysis. We conclude that the manner in which cancers instantiate a proliferative pattern of expression following oncogenesis is diverse and we find no uniform proliferative program among the cancers in this analysis.