We previously reported that HDAC9 expression was significantly lower in ERα‐positive breast cancer cell lines, such as MCF7 and T47D, compared with ERα‐negative breast cancer cell lines, such as MDA‐MB231 and MDA‐MB436 (Fig. 1E) (Lapierre et al., 2016). The gene discussed is ESR1; the disease is breast carcinoma.