Effects of drug combinations on HRGβ1-driven 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), gefitinib (1 μM), trastuzumab (100 nM), LY294002 (10 μM) or a combination of these agents. Results expressed as the mean ± standard error of the mean of triplicate wells and are representative of three separate experiments. Tamoxifen was present in all studies. *P < 0.05, **P < 0.01 and ***P < 0.001 versus control; ††
P < 0.01 and †††
P < 0.001 versus HRGβ1; §
P < 0.05 and §§§
P < 0.001 versus gefitinib + HRGβ1.