Screening mammography use among current, former, and never hormone therapy users may not explain recent declines in breast cancer incidence.
BACKGROUND
Screening mammography and invasive breast cancer and ductal carcinoma in situ (DCIS) rates recently declined in the United States; screening mammography declines among former hormone therapy (HT) users may be an important contributor. We longitudinally examined women and compared mammography use and cancer rates by HT use [current, former, and never users of estrogen + progestin (EPT) and estrogen only (ET)].


METHODS
We studied 163,490 unique women aged 50-79 years enrolled in Group Health (Washington State) between 1994-2009. Electronic data identified HT dispensing, mammography use and incident breast cancer diagnosis. We calculated age-adjusted screening compliance as a time-varying variable (screened-within-the-past-26 months, yes/no).


RESULTS
Before 2002, screening compliance differed significantly by HT with current EPT users having the highest rates (83%) followed by former EPT (77%), current ET (77%), former ET (72%), and never users (56%). After 2002, screening was high (∼81%) among current and former EPT and ET users and significantly increased among never users (∼62%). Invasive breast cancer rates significantly decreased over the whole study period (P(trend) ≤ 0.05) for all HT users, except EPT current users (P(trend) = 0.68); DCIS rates did not change in any group.


CONCLUSIONS
Differential screening mammography rates by HT use do not explain invasive breast cancer incidence declines. Our data suggest discontinuing HT has an immediate effect on breast cancer rates, lending support to the mechanism that cessation leads to tumor regression.


CONCLUSIONS
Studies examining the influence of a changing exposure in relation to outcomes should account for varying exposures, individuals' characteristics, as well as screening methods and frequency.
Group Health Research Institute, Group Health Cooperative, Seattle, WA 98101, USA. buist.d@ghc.org
Diana S M
DS
Buist
Rod
R
Walker
Erin J Aiello
EJ
Bowles
Patricia A
PA
Carney
Stephen H
SH
Taplin
Tracy
T
Onega
Karla
K
Kerlikowske
Walter
W
Clinton
Diana L
DL
Miglioretti
D000368:Aged; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000453:epidemiology* / Q000517:prevention & control; D002285:Carcinoma, Intraductal, Noninfiltrating / Q000000981:diagnostic imaging* / Q000453:epidemiology*; D015331:Cohort Studies; D055088:Early Detection of Cancer / Q000379:methods / Q000706:statistics & numerical data; D005260:Female; D020249:Hormone Replacement Therapy / Q000706:statistics & numerical data; D006801:Humans; D015994:Incidence; D008137:Longitudinal Studies; D008327:Mammography / Q000379:methods / Q000706:statistics & numerical data*; D008403:Mass Screening; D008875:Middle Aged; D018426:SEER Program; D014861:Washington / Q000453:epidemiology