title: Chordoma dedifferentiation after proton beam therapy: a case report and review of the literature.
abstract: BACKGROUND
  Chordoma is a rare invasive bone tumor that may occur anywhere along the neuraxis. A total of three primary histological varieties have been identified: conventional, chondroid, and dedifferentiated.
  
  
  METHODS
  We report a case of an 8-year-old white girl who presented with conventional chordoma, was treated with surgical resection and mixed proton and photon beam therapy, and had a recurrence in the resection cavity 2.5 years later with dedifferentiated morphology. The recurrent tumor did not express brachyury, a recently identified protein specific to tissue of notochordal origin.
  
  
  CONCLUSIONS
  The short time period between radiation therapy and dedifferentiation, low dose of photons, and rarity of dedifferentiated skull base chordomas in pediatric patients should alert clinicians to the possibility of chordoma dedifferentiation after proton beam therapy.
authors.affiliation: University of Arizona College of Medicine, 1501 N Campbell Ave, Tucson, AZ, 85724, USA. jfrankl@email.arizona.edu.
authors.forename: Joseph
authors.identifier: http://orcid.org/0000-0002-0156-3150
authors.initials: J
authors.lastname: Frankl
authors.affiliation: Department of Pathology, University of Arizona College of Medicine, 1501 N Campbell Ave, Tucson, AZ, 85724, USA.
authors.forename: Cassi
authors.initials: C
authors.lastname: Grotepas
authors.affiliation: Department of Radiation Oncology, University of Arizona College of Medicine, 1501 N Campbell Ave, Tucson, AZ, 85724, USA.
authors.forename: Baldassare
authors.initials: B
authors.lastname: Stea
authors.affiliation: Department of Surgery, University of Arizona College of Medicine, 1501 N Campbell Ave, Tucson, AZ, 85724, USA.
authors.forename: G Michael
authors.initials: GM
authors.lastname: Lemole
authors.affiliation: Department of Otolaryngology - Head and Neck Surgery, University of Arizona College of Medicine, 1501 N Campbell Ave, Tucson, AZ, 85724, USA.
authors.forename: Alexander
authors.initials: A
authors.lastname: Chiu
authors.affiliation: Department of Medical Imaging, University of Arizona College of Medicine, 1501 N Campbell Ave, Tucson, AZ, 85724, USA.
authors.forename: Rihan
authors.initials: R
authors.lastname: Khan
mesh_terms: D014408:Biomarkers, Tumor; D054337:Cell Dedifferentiation / Q000502:physiology / Q000528:radiation effects*; D045744:Cell Line, Tumor; D002648:Child; D002817:Chordoma / Q000000981:diagnostic imaging / Q000473:pathology* / Q000628:therapy; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D009364:Neoplasm Recurrence, Local / Q000473:pathology* / Q000601:surgery; D061766:Proton Therapy; D011829:Radiation Dosage; D018714:Radiotherapy, Adjuvant; D012509:Sarcoma / Q000000981:diagnostic imaging* / Q000473:pathology; D019292:Skull Base Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology* / Q000628:therapy
chemical_list: D014408:Biomarkers, Tumor
keywords: Case report; Chordoma; Dedifferentiation; Oncology; Pediatric tumors; Proton beam therapy