Neu-YD strain exhibits decreased invasion, intravasation and metastasis compared to Neu-NDL and Neu-YB strains. (A) The in vivo invasion assay was performed, allowing tumor cells to invade over 4 hours into microneedles containing 25 nM epidermal growth factor (EGF) or buffer. Neu-NDL = Neu deletion mutant (activated receptor). Data are means and SEM. **P < 0.005 by t-test, n = three to five mice per strain and five to seven needles per condition. (B) A blood burden assay was performed to evaluate intravasation. The number of single cells per milliliter of blood were counted. Data are means and SEM. *P < 0.05 by t-test, n = 8 to 11 mice per strain. (C) H & E-stained sections (5 μm each) spaced 250 μm apart were taken from the whole lung sample, and metastases were counted in every section. The efficiency of lung metastasis is represented as the total number of metastases in all lung sections for each animal that had metastases. Data are means and SEM. *P < 0.05 and ** p < 0.005 by Mann-Whitney U test; n = 16 Neu-NDL mice, 15 Neu-YD mice and 8 Neu-YB mice.