To evaluate whether and how the expression of the RET gene and its co-receptors and ligands depends on estrogen levels in BC cell lines, we treated both MCF7 and T47D with 17-β-estradiol for 6 and 24 hours and performed a realtime PCR for RET, GFRa1, ARTN, and NRTN genes. The gene discussed is RET; the disease is breast cancer.