The ectopic expression of ErbB2 in non-invasive MCF7, SUM149, or SUM159 breast cancer cell lines increases the proportion of CSC’s and invasion in vitro and facilitates mammosphere formation and appearance of ductal structures in primary tumors in immunocompromised NOD-SCID mice [166], however inducing only occasional metastasis in vivo [167]. The gene discussed is ERBB2; the disease is breast cancer.