title: Metformin may be associated with false-negative cancer detection in the gastrointestinal tract on PET/CT.
abstract: OBJECTIVE
  Concurrent therapy with the antihyperglycemic drug metformin can hinder the detection of malignancy in the abdominal and pelvic portions of 18F-fluordeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) imaging performed for the diagnosis or staging of malignancy, as well as for treatment response and radiation therapy planning. This is due to the metformin-induced increase in intestinal FDG radiotracer uptake. We aim to bring this potentially important interaction to the attention of clinicians who care for cancer patients with diabetes.
  
  
  METHODS
  We searched MEDLINE (from 1970 to January 2014) and Google Scholar for relevant English-language articles using the following search terms: "metformin and FDG/PET, metformin and bowel uptake, metformin, and cancer, metformin and the intestine, metformin pharmacokinetics, hyperglycemia and FDG/PET." We reviewed the reference lists of pertinent articles with respect to metformin gut physiology, impact on FDG uptake and the effect on diagnostic accuracy of abdominalpelvic PET/CT scans with concurrent metformin therapy.
  
  
  RESULTS
  We reviewed the action of metformin in the intestine, with particular emphasis on the role of metformin in PET/CT imaging and include a discussion of clinical studies on the topic to help refine knowledge and inform practice. Finally, we discuss aspects pertinent to the management of type 2 diabetes (T2D) patients on metformin undergoing PET/CT.
  
  
  CONCLUSIONS
  Metformin leads to intense, diffusely increased FDG uptake in the colon, and to a lesser degree, the small intestine, which limits the diagnostic capabilities of FDG PET/CT scanning and may mask gastrointestinal malignancies. We suggest that metformin be discontinued 48 hours before FDG PET/CT scanning is performed in oncology patients. More rigorous data are needed to support the widespread generalizability of this recommendation.
authors.affiliation: Section of Endocrinology, Diabetes and Nutrition, Boston Medical Center, Boston University School of Medicine.
authors.forename: Devin W
authors.initials: DW
authors.lastname: Steenkamp
authors.affiliation: Division of Endocrinology, Diabetes and Hypertension, Brigham and Women's Hospital, Harvard Medical School.
authors.forename: Marie E
authors.initials: ME
authors.lastname: McDonnell
authors.affiliation: Section of Nuclear Medicine, Department of Radiology, Boston Medical Center/Boston University School of Medicine, Boston, Massachusetts.
authors.forename: Sara
authors.initials: S
authors.lastname: Meibom
mesh_terms: D003924:Diabetes Mellitus, Type 2; D005188:False Negative Reactions; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008687:Metformin; D009369:Neoplasms / Q000000981:diagnostic imaging*; D000072078:Positron Emission Tomography Computed Tomography; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D014057:Tomography, X-Ray Computed
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D008687:Metformin