ESR1 and breast cancer: Even in breast cancer, a tumor suppressor activity has been suggested, as higher levels of the longer transcript of ZFHX3 (ZFHX3-A) correlate with markers of better prognosis such as negative lymph node involvement, lower tumor grade, and smaller tumor size [17]; and in ER+/PR+ breast cancer cell lines MCF-7 and T-47D cultured in a hormone-free medium, ZFHX3 was inhibitory to estrogen-mediated cell proliferation in 2D culture [20].