Heterozygous Beclin 1 (beclin 1+/- mutant) was shown to have a high incidence of spontaneous tumors [289,293], whilst Beclin 1 inhibited tumor growth in cell lines such as the breast cancer cell line, MCF-7, in which Beclin 1 expression was lower than in normal epithelial breast cells [294]. The gene discussed is BECN1; the disease is breast cancer.