title: Estrogen-progestin use and breast cancer characteristics in lean and overweight postmenopausal women.
abstract: OBJECTIVE
  Breast cancer associated with estrogen-progestin (EP) therapy may have more favorable characteristics than cancer in never users, but results are conflicting. It is not well known either whether Body Mass Index (BMI) modifies this association. We investigated breast cancer characteristics in EP users for lean (BMI < 25 kg/m2) and overweight women (BMI ≥ 25 kg/m2).
  
  
  METHODS
  The Icelandic Cancer Detection Clinic cohort, with information on breast cancer risk factors for 90% of Icelandic women, was linked with the population-based Icelandic Cancer Registry. A total of 781 women with invasive breast cancer diagnosed 51 years or older were matched with 7761 controls from the cohort. Conditional logistic regression was used for estimating adjusted odds ratios (OR) and 95% confidence intervals (CI) according to tumor characteristics, stratified by BMI. Polytomous logistic regression was applied in a case-only analysis for testing whether the risk associated with EP use differed according to tumor characteristics.
  
  
  RESULTS
  Ever EP users had a twofold higher risk of breast cancer compared with never users (OR 2.05, 95% CI 1.71-2.45). In lean women, EP use was significantly less likely to be associated with grade 2 or 3 tumors than grade 1 tumors, contrary to overweight women for whom risk was increased irrespective of grade. EP use in overweight women was associated with a higher risk of lobular than ductal cancer (OR 2.75, 95% CI 1.29-5.87).
  
  
  CONCLUSIONS
  Among lean EP users, tumor characteristics were more favorable than among never users. This effect was not observed for overweight women.
authors.affiliation: Department of Clinical Oncology, Beatson West of Scotland Cancer Centre, Glasgow, UK.|Department of Internal Medicine, Landspitali University Hospital, Reykjavik, Iceland.|Icelandic Cancer Registry, Icelandic Cancer Society, Reykjavik, Iceland.
authors.forename: Olof J
authors.initials: OJ
authors.lastname: Kjartansdottir
authors.affiliation: Department of Education and Prevention, Icelandic Cancer Society, Reykjavik, Iceland.
authors.forename: Lara G
authors.initials: LG
authors.lastname: Sigurdardottir
authors.affiliation: Icelandic Cancer Registry, Icelandic Cancer Society, Reykjavik, Iceland.
authors.forename: Elinborg J
authors.initials: EJ
authors.lastname: Olafsdottir
authors.affiliation: Department of Pathology, Landspitali University Hospital, Reykjavik, Iceland.|Faculty of Medicine, University of Iceland, Reykjavik, Iceland.
authors.forename: Jon G
authors.initials: JG
authors.lastname: Jonasson
authors.affiliation: Cancer Registry of Norway, Institute of Population-Based Cancer Research, Oslo, Norway.|Department of Preventive Medicine, University of Southern California, Los Angeles, CA, USA.|Department of Nutrition, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.
authors.forename: Giske
authors.initials: G
authors.lastname: Ursin
authors.affiliation: Icelandic Cancer Registry, Icelandic Cancer Society, Reykjavik, Iceland. laufeyt@krabb.is.|Faculty of Medicine, University of Iceland, Reykjavik, Iceland. laufeyt@krabb.is.
authors.forename: Laufey
authors.initials: L
authors.lastname: Tryggvadottir
mesh_terms: D001943:Breast Neoplasms / Q000453:epidemiology* / Q000473:pathology; D018270:Carcinoma, Ductal, Breast / Q000453:epidemiology* / Q000473:pathology; D018275:Carcinoma, Lobular / Q000453:epidemiology* / Q000473:pathology; D016022:Case-Control Studies; D015914:Estrogen Replacement Therapy; D004967:Estrogens / Q000494:pharmacology / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D008875:Middle Aged; D050177:Overweight / Q000453:epidemiology / Q000473:pathology; D011372:Progestins / Q000494:pharmacology / Q000627:therapeutic use*; D011446:Prospective Studies
chemical_list: D004967:Estrogens; D011372:Progestins
keywords: Body Mass Index; Breast cancer; Estrogen; Menopausal hormone therapy; Progesterone; Tumor characteristics