Dontu et al. (2004) have reported a 10-fold increase in secondary mammosphere formation upon the addition of a Notch-activating delta-Serrate-Lag2 peptide. Notch inhibition decreases ductal carcinoma in situ-derived mammosphere production (Farnie and Clarke, 2007). Notch 3 is involved in mammosphere formation (Sansone et al., 2007). Moreover, positive feedback between Notch 3 and TGF-β contributes to the metastasis of breast and lung cancers (Zhang et al., 2010; Liu et al., 2014). The gene discussed is NOTCH3; the disease is lung cancer.