ESR1 and neoplasm: Antibodies against these two proteins were used here for sequential dual FACS of another set of T47Dco mouse tumor-derived cells to generate two new, isogenic, pure cell lines: pLB are CLD3– CD49f+ and ER–PR–CK5+; pLUM are CLD3+ CD49f– and ER+PR+CK5– (Figure 1).