Within this shortlist are known regulators of breast cancer progression and metastasis such as matrix metallopeptidase 9 (Mmp9)16, cathepsin D (Ctsd)17, insulin-like growth factor 1 (Igf1)18 and MET (Met)19, as well as inhibitors of apoptosis such as BCL2-like 2 (Bcl2l), BCL2-associated athanogene 1 (Bag1), nucleolar protein 3 (Nol3) and protein kinase C eta (Prkch), providing confidence in the ability of the screen to uncover novel metastatic regulators. Here, CTSD is linked to breast cancer.