CCND1 and idiopathic pulmonary fibrosis: The reason for the observed elevated levels of cyclin D1 in IPF cells lines is as yet unknown and will be addressed in separate lung tissue studies; however possibilities include amplification of gene copy number, hyper-stimulation of the RhoA pathway through an aberrant disease-associated mutation (or pathogenic mutation causing abrogation of pathway inhibitors) or simply, factor/s within the profibrogenic milieu.