H2AX and Patent ductus arteriosus: Further characterization of the tumors and metastases revealed expression of PDA markers, such as CK19 (Fig. 2C), high proliferative index as measured by Ki67 staining (Fig. 2D), accumulation of mutant p53 protein (Fig. 2E), genomic instability as detected by γ-H2AX expression (Fig. 2F), and accumulation of desmoplastic stroma including smooth muscle actin-expressing fibroblasts (Fig. 2G).