Evidence for clonal fibroblast proliferation and autoimmune process in idiopathic retroperitoneal fibrosis L. Cheng * , J. Clevenger, A. Lopez-Beltran * Indiana University, Dept. of Pathology, Indianapolis, USA Objective: We sought to determine if idiopathic retroperitoneal fibrosis is clonal process and if it is an autoimmune, or IgG4-driven, process. Method: Thirty cases of idiopathic retroperitoneal fibrosis, in whom known causes of retroperitoneal fibrosis were excluded and those for which paraffin blocks were available, were included in this study. We performed clonality analysis in 16 female patients. Genomic DNA samples were prepared from formalin-fixed, paraffin-embedded tissue sections using laser capture microdissection.