The average tumor volumes were significantly elevated (approximately 1.5-fold increase) for ER-expressing 4T1.2 (900 mm3)- and ER-expressing E0771/Bone (1677 mm3)-derived tumors when compared with the tumors derived from the TN parental cell lines (658 mm3 and 1029 mm3, respectively; two-way ANOVA, p < 0.05, Figure 5). Here, ESR1 is linked to neoplasm.