Effects of HRGβ1 and gefitinib on tamoxifen-resistant MCF-7 cell growth and invasion. (a) Growth and (b) invasive capacity of tamoxifen-resistant MCF-7 (Tam-R) cells, on day 7 for growth and on day 3 for invasion, following treatment with either HRGβ1 (10 ng/ml) or gefitinib (1 mM) or a combination of the two agents. Results expressed as the mean ± standard error of the mean of triplicate wells and are representative of at least three separate experiments. **P < 0.01 versus control, ***P < 0.001 versus control, †
P < 0.05 versus gefitinib, †††
P < 0.001 versus gefitinib.