Mammosphere assays provide an assay of stem cell potential, wherein formation of secondary mammospheres (i.e., derived from dissociated and serially passaged primary mammospheres) is a definitive assay of the ability of minority breast cancer cell stem cells within a heterogeneous population to expand and reestablish as E-cadherin-positive spheres able to grow in suspension culture following long-term serial passage as non-adherent cells [73]. The gene discussed is CDH1; the disease is breast cancer.