ERBB2 and breast cancer: Compared to tetO/Neu mice, p190B mice formed more mammary tumors in number 1 (44+/-10 vs. 11+/-7 percent of mice, P = 0.013), and number 4 (44 +/- 10 vs. 16 +/- 9 percent of mice, P = 0.042) mammary gland pairs.