To examine whether FRMD8 plays a role in breast tumorigenesis, we established luminal epithelium-specific Frmd8 knockout mice (MMTV-Cre+; Frmd8fl/fl) (Figure 1A and B) and further generated a Frmd8-deletion breast cancer mouse model (MMTV-Cre+; Frmd8fl/fl; PyMT) by crossing MMTV-Cre+; Frmd8fl/fl mice with MMTV-PyMT (PyMT) mice, a widely used transgenic mouse model of mammary tumorigenesis (Figure 1C and D, Figure 1—figure supplement 1A and B). Here, FRMD8 is linked to breast carcinoma.