Likewise, the loss of Lhx4 does not affect ISL1 expression in developing BCs, whereas LHX3 expression is greatly reduced (Figures 5C, 5F, and S4A–S4C), suggesting that Isl1 and Lhx4 function in parallel and upstream of Lhx3 in regulating BC development. Here, LHX4 is linked to breast cancer.