Genes over-expressed by stem-like tumors were especially enriched (p<0.0001) for gene sets describing poor prognosis and undifferentiated cancers; high-grade, invasive ovarian cancer; Myc targets; and embryonic stem cells, BRCA1 mutation, estrogen receptor (ER)-negative status, and the basal-like subtype in breast cancer (Table S5). Here, ESR1 is linked to breast cancer.