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Reduced risk of breast cancer mortality in women using postmenopausal hormone therapy: a Finnish nationwide comparative study

Mikkola, Tomi S. MD, PhD; Savolainen-Peltonen, Hanna MD, PhD; Tuomikoski, Pauliina MD, PhD; Hoti, Fabian PhD; Vattulainen, Pia MSc; Gissler, Mika M.SocSci, PhD; Ylikorkala, Olavi MD, PhD

doi: 10.1097/GME.0000000000000698
Original Articles

Objective: 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).

Methods: 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.

Results: 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.

Conclusions: 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.

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.

Address correspondence to: Tomi S. Mikkola, MD, PhD, Department of Obstetrics and Gynecology, Helsinki University Hospital, Haartmaninkatu 2, PO Box 140, FIN-00029 HUS, Helsinki, Finland. E-mail: tomi.mikkola@hus.fi

Received 23 December, 2015

Revised 18 April, 2016

Accepted 18 April, 2016

The funding sources had no role in study design, collection, analysis or interpretation of the data, writing of the article, or the decision to submit the article for publication.

Funding/support: The present study was supported by Helsinki University Hospital Research Grant and Jane and Aatos Erkko Foundation.

Financial disclosure/conflicts of interest: T.S.M. has been a speaker and/or received consulting fees from Mylan and Novo Nordisk. H.S.-P. has been a speaker for Mylan and received funding for congress trips from Mylan and Finox Biotech. P.T. has been a speaker and/or received consulting fees from Mylan and Orion, and received funding for congress trips from Mylan. F.H. and P.V. work for EPID Research. EPID Research is a company that provides financially supported studies to several pharmaceutical companies. M.G. and O.Y. have nothing to disclose.

© 2016 by The North American Menopause Society.