ESR1 and breast cancer: Furthermore, we also show for the first time that SM6Met, in the presence of E2, was able to inhibit ER+ breast cancer cell invasion to a greater extent than the SOC therapy, 4-OH-Tam alone and that the addition of SM6Met to 4-OH-Tam, further increased the inhibition of ER+ breast cancer cell invasion, to a level beyond that of SM6Met or 4-OH-Tam alone.