The response of breast cancer cells to steroid and peptide growth factors.

Four breast cancer cell lines covering a wide range of receptor characteristics were examined for their growth responses to oestradiol, insulin, EGF and the anti-oestrogen, tamoxifen. Stimulated cellular growth using both the MTT assay and 3H-thymidine incorporation into DNA, was measured against controls grown in a steroid reduced environment. The ER positive MCF-7 cell line showed clear growth responses to E2, insulin and EGF. This was also demonstrated, although to a lesser extent in the ZR-75-1 line which expresses lower levels of ER. In combination, these factors gave an additive growth response but the addition of EGF to maximal concentrations of insulin and oestradiol produced no further increase in growth. In contrast to these results, the two ER negative cell lines examined, MCF-7 Adr and MDA-MB-231 showed no growth response to exogenously applied steroids and in the case of MCF-7 Adr high concentrations of EGF were able to inhibit the growth of this cell line. They also showed high rates of growth in a steroid depleted environment which tends to suggest these cells are growing autonomously through autocrine growth factor induction.