As a tumor promoter, miR-let-7b has been found to enhance cell proliferation, adhesion, and invasion by targeting the genes of PKA1, DIAPH2, RDX, RAS, MYC, and HMGA2 and respective proteins, creating an unbalance between hyperproliferative and apoptosis-resistant phenotype of PAAF, PAEC and PASMC in IPAH. The gene discussed is HMGA2; the disease is neoplasm.