WNT1 and breast cancer: Using the classic MMTV-Wnt1 mouse mammary tumor model, Cleary et al. [22] observed that breast cancer can propagate only when its two genetically distinct subclones, luminal Wnt1highHRaswild-type and basal Wnt1lowHRasmutant, are transplanted together into mammary fat pads of wild-type host animals.