PIK3CA and vascular malformation: To mimic the congenital PIK3CA-driven vascular malformations, we first induced Pik3caH1047R expression in LECs and/or BECs during embryonic development by administering 4-hydroxytamoxifen (4-OHT) to pregnant females at embryonic day (E) 10 or 11 (Fig. 1 A).