title: Type and duration of exogenous hormone use affects breast cancer histology.
abstract: BACKGROUND
  It is unclear whether hormone replacement therapy (HRT), in addition to increasing risk for breast cancer, affects the type of breast cancer diagnosed. We conducted this investigation to assess whether the type of hormone used (none, estrogen, progesterone, or combined) and duration of use influences subsequent breast cancer histology.
  
  
  METHODS
  We performed a retrospective cohort analysis among women listed as incident cases of breast malignancy in the Kaiser Permanente Northern California Cancer Registry during 2003 (n = 2830). Type and duration of hormone used (none, estrogen, progesterone, or combined) before breast cancer diagnosis was obtained from electronic pharmacy records. The association between type and duration of hormone use with characteristics of subsequent breast cancers was examined.
  
  
  RESULTS
  Among women aged >50 years (n = 1701), any use of estrogen, progesterone, or combination therapy was not associated with an increased risk of estrogen receptor (ER)-positive disease. However, >6 months' use of combined HRT increased the odds of ER-positive tumors (odds ratio, 1.65; 95% confidence interval, 1.07-2.5; P = .02). Estrogen HRT patients were more likely than nonusers to present with low-grade (P = .05), and early-stage tumors (P = .03). This trend was not seen in combined HRT users.
  
  
  CONCLUSIONS
  Short-duration HRT did not increase the likelihood of ER-positive breast cancer. However, prolonged duration of combined HRT, but not estrogen or progesterone alone, resulted in a marked increase in ER-positive disease. Our findings suggest that the effect of combined HRT on breast cancer incidence or progression is not immediate and that long-term use is more likely to affect breast cancer histology.
authors.affiliation: Department of Surgery, Kaiser Permanente Oakland Medical Center, Oakland, California, 94602, USA.
authors.forename: Anjali S
authors.initials: AS
authors.lastname: Kumar
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Cureton
authors.forename: Veronica
authors.initials: V
authors.lastname: Shim
authors.forename: Theadora
authors.initials: T
authors.lastname: Sakata
authors.forename: Dan H
authors.initials: DH
authors.lastname: Moore
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Benz
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Esserman
authors.forename: E Shelley
authors.initials: ES
authors.lastname: Hwang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000473:pathology*; D015331:Cohort Studies; D015914:Estrogen Replacement Therapy; D005260:Female; D020249:Hormone Replacement Therapy / Q000379:methods*; D006801:Humans; D008875:Middle Aged; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D012042:Registries; D012189:Retrospective Studies; D013997:Time Factors
chemical_list: D011960:Receptors, Estrogen; D011980:Receptors, Progesterone