ISL1 and breast cancer: Interestingly, LHX family TFs (LHX3 and LHX4) made discrepant contributions to BC/PH lineage specification, with LHX4, not LHX3, exhibiting a considerable regulatory effect on BC‐specific BHLHE22 and VSX1 (Figure 6F), which was consistent with the maturity regulation of Lhx4 and Isl1 on BC subtypes in mice.[23]