ERBB2 and neoplasm: This intrinsic gene set was then used to cluster and segregate the tumours into four major subgroups: (1) a ‘luminal cell-like’ group expressing the ER, (2) a ‘basal cell-like’ group expressing keratins 5 and 17, integrinβ4, and laminin, but lacking ER expression, (3) an Erb-B2-positive subset, and (4) a ‘normal’ epithelial group.