ERBB4 and neoplasm: In agreement with these published results, here we show that, relative to control constructs, the ErbB4 Q646C mutant inhibits clonogenic proliferation of (or displays tumor suppressor activity in) MCF7 human breast tumor cells (Figure 2a and 2b, Table 1) and of MCF10A human breast epithelial cells (Figure 2c, Table 2).