Of interest, the FOXM1 activity-regulating compounds described in this manuscript were able to function as suppressors of breast cancer cell proliferation and the expression of FOXM1-signature genes and gene ontologies in a broad range of breast cancer subtypes, both hormone receptor-positive (such as MCF7 and tamoxifen-resistant MCF7) and triple negative (such as DT22 and MDA-MB-231), as well as in BT474 (ER-positive, HER2-positive) cells, where similar IC50 concentrations for inhibition of cell proliferation and FOXM1-regulated gene expressions were observed. The gene discussed is ESR1; the disease is breast cancer.