Given our previous work showing a clinically better response of ERβ1-expressing ERα-positive breast tumors to AET and, conversely, increased late recurrence rate of ERα/ERβ2-expressing tumors [30], we assessed the response of MCF7-ERβ1 and MCF7-ERβ2 cells to OHT and ICI. The gene discussed is ESR1; the disease is breast neoplasm.