title: Low-grade myofibroblastic proliferations of the urinary bladder.
abstract: BACKGROUND
  Myofibroblastic proliferations of the urinary bladder, which share some similarities with nodular fasciitis, were first reported in 1980. Since then, they have had several designations, the most frequently used being inflammatory myofibroblastic tumor. Based on both histopathologic and prognostic grounds, some authors prefer the term pseudosarcomatous myofibroblastic proliferation, at least for some of the proliferations. These same scientists also assimilate the so-called postoperative spindle cell nodules with the pseudosarcomatous myofibroblastic proliferations. Little is known about these low-grade myofibroblastic proliferations.
  
  
  OBJECTIVE
  To review the literature about low-grade myofibroblastic proliferations occurring in the urinary bladder.
  
  
  METHODS
  Textbooks and literature review. We obtained most of the clinicopathologic peculiarities from a patient population composed of the most-relevant, previously reported cases.
  
  
  CONCLUSIONS
  The low-grade myofibroblastic proliferations of the urinary bladder are rare lesions affecting males more often than they do females. The most-common signs and symptoms are hematuria and dysuria. Histopathologically, they are spindle cell proliferations in a loose myxoid stroma, even though compact proliferations or hypocellular fibrous patterns can be found. Immunohistochemistry is quite nonspecific, except for ALK-1 positivity (20%-89%). Fluorescence in situ hybridization has demonstrated clonal genetic aberrations involving the ALK gene in 50% to 60% of cases. After surgery, only 6% of patients experience local recurrence, without metastases or deaths from the disease. Malignant transformation has been reported exceptionally. These myofibroblastic proliferations are probably part of a continuum with, at one end, benign pseudosarcomatous proliferations and, at the opposite end, more-aggressive lesions. Because of the frequently indolent clinical course, aggressive treatment would be unjustified.
authors.affiliation: Department of Oncology, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Arcispedale Santa Maria Nuova, Reggio Emilia, Italy.
authors.forename: Sara
authors.initials: S
authors.lastname: Alquati
authors.forename: Federica Alessandra
authors.initials: FA
authors.lastname: Gira
authors.forename: Veronica
authors.initials: V
authors.lastname: Bartoli
authors.forename: Sandro
authors.initials: S
authors.lastname: Contini
authors.forename: Domenico
authors.initials: D
authors.lastname: Corradi
mesh_terms: D000077548:Anaplastic Lymphoma Kinase; D049109:Cell Proliferation; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007249:Inflammation / Q000378:metabolism / Q000473:pathology; D008297:Male; D058628:Myofibroblasts / Q000378:metabolism / Q000473:pathology*; D009379:Neoplasms, Muscle Tissue / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D001743:Urinary Bladder / Q000378:metabolism / Q000473:pathology*; D001749:Urinary Bladder Neoplasms / Q000201:enzymology / Q000235:genetics / Q000473:pathology
chemical_list: C000626173:ALK protein, human; D000077548:Anaplastic Lymphoma Kinase; D020794:Receptor Protein-Tyrosine Kinases