A Novel Subset of Human Tumors That Simultaneously Overexpress Multiple E2F-responsive Genes Found in Breast, Ovarian, and Prostate Cancers

Reasoning that overexpression of multiple E2F-responsive genes might be a useful marker for RB1 dysfunction, we compiled a list of E2F-responsive genes from the literature and evaluated their expression in publicly available gene expression microarray data of patients with breast cancer, serous ovarian cancer, and prostate cancer. In breast cancer, a group of tumors was identified, each of which simultaneously overexpressed multiple E2F-responsive genes. Seventy percent of these genes were concerned with cell cycle progression, DNA repair, or mitosis. These E2F-responsive gene overexpressing (ERGO) tumors frequently exhibited additional evidence of Rb/E2F axis dysfunction, were mostly triple negative, and preferentially overexpressed multiple basal cytokeratins, suggesting that they overlapped substantially with the basal-like tumor subset. ERGO tumors were also identified in serous ovarian cancer and prostate cancer. In these cancer types, there was no evidence for a tumor subset comparable to the breast cancer basal-like subset. A core group of about 30 E2F-responsive genes were overexpressed in all three cancer types. Thus, it appears that disorders of the Rb/E2F axis can arise at multiple organ sites and produce tumors that simultaneously overexpress multiple E2F-responsive genes.