ERBB2 and neoplasm: Whereas greater than 90% of HER2/neu-Prim1 and Wnt1-Prim1 primary tumor cells were labeled with BrdU over the 2-week period prior to sacrifice, fewer than 9% of HER2/neu-Prim1 and Wnt1-Prim1 residual tumor cells incorporated BrdU over the same time period (Fig. 2b, c, e, f).