title: Skeletal muscle fiber size and fiber type distribution in human cancer: Effects of weight loss and relationship to physical function.
abstract: Cancer patients frequently experience weight loss, with negative consequences for functionality and prognosis. The extent to which muscle atrophy contributes to weight loss, however, is not clear, as few studies have directly measured muscle fiber morphology in cancer patients.
  
  
  
  Whole body and regional tissue composition were measured, along with the cross-sectional area (CSA) and fiber type of mechanically-isolated, single muscle fibers, in 19 cancer patients (8 with a history of weight loss, 11 weight-stable) and 15 non-diseased controls.
  
  
  
  Whole body fat mass was reduced in cancer patients with a history of weight loss, but no differences in whole body or leg fat-free mass were apparent. In contrast, reductions (∼20%) in single muscle fiber CSA were found in both slow-twitch, myosin heavy chain (MHC) I and fast-twitch, MHC IIA fibers in both weight-stable patients and those with a history of weight loss. Fiber type distribution showed a shift towards a fast-twitch phenotype compared to controls, which may preserve muscle function in cancer patients despite atrophy, as positive relationships were found between the fractions of hybrid MHC IIAX and I/IIA fibers and 6-min walk performance.
  
  
  
  Our results suggest that, although not apparent from whole body or regional measurements, cancer is associated with reduced skeletal muscle fiber size independent of weight loss history and a shift towards fast-twitch fibers, phenotypes that resemble adaptations to muscle disuse.
authors.affiliation: Department of Medicine, University of Vermont, College of Medicine, Burlington, VT, USA; Department of Molecular Physiology and Biophysics, University of Vermont, College of Medicine, Burlington, VT, USA; Department of Orthopaedics and Rehabilitation, University of Vermont, College of Medicine, Burlington, VT, USA. Electronic address: michael.toth@uvm.edu.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Toth
authors.affiliation: Department of Medicine, University of Vermont, College of Medicine, Burlington, VT, USA.
authors.forename: Damien M
authors.initials: DM
authors.lastname: Callahan
authors.affiliation: Department of Molecular Physiology and Biophysics, University of Vermont, College of Medicine, Burlington, VT, USA.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Miller
authors.affiliation: Department of Orthopaedics and Rehabilitation, University of Vermont, College of Medicine, Burlington, VT, USA.
authors.forename: Timothy W
authors.initials: TW
authors.lastname: Tourville
authors.affiliation: Department of Medicine, University of Vermont, College of Medicine, Burlington, VT, USA.
authors.forename: Sarah B
authors.initials: SB
authors.lastname: Hackett
authors.affiliation: Department of Surgery, University of Vermont, College of Medicine, Burlington, VT, USA.
authors.forename: Marion E
authors.initials: ME
authors.lastname: Couch
authors.affiliation: Department of Medicine, University of Vermont, College of Medicine, Burlington, VT, USA.
authors.forename: Kim
authors.initials: K
authors.lastname: Dittus
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018656:Muscle Fibers, Fast-Twitch / Q000473:pathology; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000145:classification* / Q000473:pathology*; D018657:Muscle Fibers, Slow-Twitch / Q000473:pathology; D009133:Muscular Atrophy / Q000209:etiology / Q000473:pathology; D018995:Myosin Heavy Chains / Q000032:analysis; D009369:Neoplasms / Q000150:complications / Q000473:pathology* / Q000503:physiopathology; D011379:Prognosis; D015431:Weight Loss
chemical_list: D018995:Myosin Heavy Chains
keywords: Atrophy; Fatigue; Single muscle fiber