The cancer paradigm of severe pulmonary arterial hypertension.

The plexiform lesions of severe pulmonary arterial hypertension (PAH) are similar in histologic appearance, whether the disease is idiopathic or secondary. Both forms of the disease show actively proliferating endothelial cells without evidence of apoptosis. Here, we discuss the pathobiology of the atypical, angioproliferative endothelial cells in severe PAH. The concept of the endothelial cell as a "quasi-malignant" cell provides a new framework for antiproliferative, antiangiogenic therapy in severe PAH.