title: Reduced risk of breast cancer mortality in women using postmenopausal hormone therapy: a Finnish nationwide comparative study.
abstract: Data are controversial on the impact of postmenopausal hormone therapy (HT) on breast cancer mortality. We analyzed nationwide Finnish data on breast cancer mortality risk in women using HT consisting of estradiol-only therapy (ET) or estrogen-progestogen therapy (EPT).
  
  
  
  In total, 489,105 women using HT in 1994 to 2009, traced from the nationwide reimbursement register, were followed from the HT initiation (3.3 million cumulative exposure years) to breast cancer death (n = 1,578 women). The observed deaths were compared with those in the age-standardized background population.
  
  
  
  The breast cancer mortality risk was reduced in all HT users with exposure for at most 5 years (standardized mortality ratio 0.56; CI 0.52-0.60), more than 5 to 10 years (0.46; 0.41-0.51), or more than 10 years (0.62; 0.56-0.68). A significantly larger risk reduction was detected in the 50 to 59 years age group (0.33; 0.29-0.37) compared with 60 to 69 (0.64; 0.59-0.70) or 70 to 79 (0.78; 0.69-0.87) years age groups. The death risk reductions in ET users tended to be larger in all age groups compared with EPT users, with a significant difference only in the 70 to 79 years age group (0.66; 0.57-0.76 vs 0.88; 0.77-1.00). The age at HT initiation, regardless whether ET or EPT, showed no association with breast cancer mortality.
  
  
  
  In the Finnish unselected population, breast cancer is fatal in 1 of 10 patients. Our data imply that this risk is prevalent in 1 of 20 patients with history of HT use. This is an important message for women considering or already using HT.
authors.affiliation: 1Department of Obstetrics and Gynecology, University of Helsinki and Helsinki University Hospital, Helsinki, Finland 2Folkhälsan Research Center, Biomedicum, Helsinki, Finland 3EPID Research Oy, Espoo, Finland 4Information Services Department, National Institute for Health and Welfare, Helsinki, Finland.
authors.forename: Tomi S
authors.initials: TS
authors.lastname: Mikkola
authors.forename: Hanna
authors.initials: H
authors.lastname: Savolainen-Peltonen
authors.forename: Pauliina
authors.initials: P
authors.lastname: Tuomikoski
authors.forename: Fabian
authors.initials: F
authors.lastname: Hoti
authors.forename: Pia
authors.initials: P
authors.lastname: Vattulainen
authors.forename: Mika
authors.initials: M
authors.lastname: Gissler
authors.forename: Olavi
authors.initials: O
authors.lastname: Ylikorkala
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000401:mortality*; D004958:Estradiol / Q000008:administration & dosage; D015914:Estrogen Replacement Therapy / Q000009:adverse effects / Q000379:methods*; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D008875:Middle Aged; D017698:Postmenopause; D011372:Progestins / Q000008:administration & dosage; D012307:Risk Factors
chemical_list: D011372:Progestins; D004958:Estradiol