ERBB2 and breast cancer: In this study, we demonstrate that the Wnt/PCP-specific transmembrane scaffold protein Vangl2 is vital for the efficient formation of metastatic lung lesions from ErbB2-driven mammary tumors, mediates collective cell invasion in conjunction with the permissive factor bFGF in PyMT-driven mammary tumor organoids, and is highly expressed in invasive leader cells where it appears to mediate pro-migratory protrusive activity via regulation of RhoA.