To define the role of BHLHE40 in breast cancer metastasis, we examined the effect of its knockdown (KD) by a shRNA lentiviral construct on spontaneous lung metastasis of orthotopic xenograft tumors derived from a lung metastasis-enriched subline (LM) of breast cancer MDA-MB-231 cells [28]. Here, BHLHE40 is linked to breast cancer.