FLT4 and lymphangiectasis: At P12, histologic and immunologic analyses of tamoxifen-treated KrasG12Dfl/+; Cdh5CreERT2 neonatal mice revealed aberrantly dilated peribronchial and intercostal lymphatic vessels lined by Pdpn+ and Lyve1+ or Prox1+ and Vegfr3+ endothelial cells, enlarged pulmonary alveoli, and normal lymphatic endothelial cell proliferation, consistent with human neonatal pulmonary lymphangiectasia (Figure 2, A–F).