title: High levels of dietary soy decrease mammary tumor latency and increase incidence in MTB-IGFIR transgenic mice.
abstract: BACKGROUND
  Epidemiologic data indicates that Asian diets, which are high in soy protein, reduce a women's risk of developing breast cancer. However, it has been difficult to dissociate the benefits of soy from other variables including environmental and lifestyle factors. Since prospective studies in humans would take decades to complete, rodent models provide a valuable research alternative.
  
  
  METHODS
  In this study, MTB-IGFIR transgenic mice, which develop mammary tumors resulting from overexpression of the type I insulin-like growth factor receptor (IGF-IR), were utilized. MTB-IGFIR mice were fed a soy-based or casein-based diet throughout all stages of development to reflect soy exposure in Asian cultures. Mammary tumors were initiated at 2 different developmental stages by commencing IGF-IR transgene expression either during puberty or in adult mice.
  
  
  RESULTS
  MTB-IGFIR mice fed a soy-based diet displayed increased tumor incidence and accelerated tumor onset compared to MTB-IGFIR mice fed a casein diet. Two markers of estrogen receptor signaling, Pgr and Areg, were elevated in mammary tissue from mice fed the soy diet compared to mice fed the casein diet suggesting that high levels of soy may promote mammary tumor development through acting as an estrogen receptor agonist. Mammary tumors from mice fed a soy diet more frequently expressed metaplastic markers such as cytokeratins 5 and 14 as well as p63 and displayed reduced lung metastases compared to mammary tumors from mice fed a casein diet.
  
  
  CONCLUSIONS
  Diets consisting of very high levels of soy protein promote mammary tumor development and decrease tumor latency possibly through activating estrogen receptor signaling. Additional studies are required to determine whether a more moderate amount of dietary soy can inhibit oncogene-induced mammary tumorigenesis.
authors: Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, 50 Stone Road East, Guelph, ON, N1G2W1, Canada. kawatson@uoguelph.ca.
authors: Katrina L
authors: KL
authors: Watson
authors: Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, 50 Stone Road East, Guelph, ON, N1G2W1, Canada. stalkerl@uoguelph.ca.
authors: Leanne
authors: L
authors: Stalker
authors: Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, 50 Stone Road East, Guelph, ON, N1G2W1, Canada. rjones12@uoguelph.ca.
authors: Robert A
authors: RA
authors: Jones
authors: Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, 50 Stone Road East, Guelph, ON, N1G2W1, Canada. rmoorehe@uoguelph.ca.
authors: Roger A
authors: RA
authors: Moorehead
mesh_terms: D000821:Animal Feed; D000818:Animals; D015415:Biomarkers; D002471:Cell Transformation, Neoplastic; D005260:Female; D015870:Gene Expression; D006801:Humans; D015674:Mammary Neoplasms, Animal / Q000209:etiology* / Q000378:metabolism / Q000401:mortality / Q000473:pathology*; D051379:Mice; D008822:Mice, Transgenic; D009362:Neoplasm Metastasis; D017526:Receptor, IGF Type 1 / Q000235:genetics*; D015398:Signal Transduction; D045730:Soy Foods; D047368:Tumor Burden
chemical_list: D015415:Biomarkers; D017526:Receptor, IGF Type 1
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