Ferrocifens have been designed by Jaouen et al. [26] upon replacing, by a ferrocenyl group, a phenyl group of tamoxifen 10a (Walpole, Richardson, 1962) and hydroxytamoxifen (TAM-OH, 10b), which are selective estrogen receptor modulators (SERMs), decreasing the growth of breast cancer cells. The gene discussed is ESR1; the disease is breast cancer.