Estimating age-specific breast cancer risks: a descriptive tool to identify age interactions.
OBJECTIVE
Clarifying age-specific female breast cancer risks and interactions may provide important etiologic clues.


METHODS
Using a population-based case-control study in Poland (2000-2003) of 2,386 incident breast cancer cases and 2,502 control subjects aged 25-74 years, we estimated age-specific breast cancer incidence rates according to risk factors.


RESULTS
Breast cancer risks were elevated among women with positive family history (FH), younger age at menarche, older age at first full-term birth, nulliparity, exogenous hormonal usage, and reduced physical activity (PA). Notwithstanding overall risks, we observed statistically significant quantitative (non-crossover) and qualitative (crossover) age interactions for all risk factors except for FH and PA. For example, nulliparity compared to parity reduced breast cancer risk among women ages 25-39 years then rates crossed or reversed, after which nulliparity increased relative risks among women ages 40-74 years.


CONCLUSIONS
Though quantitative age interactions could be expected, qualitative interactions were somewhat counterintuitive. If confirmed in other populations, qualitative interactions for a continuous covariate such as age will be difficult to reconcile in a sequential (multistep or monolithic) 'stochastic' breast cancer model. Alternatively, the reversal of relative risks among younger and older women suggests subgroup heterogeneity with different etiologic mechanisms for early-onset and late-onset breast cancer types.
Anderson
William F
WF
Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institute of Health, Executive Plaza South 8070, 6120 Executive Plaza Blvd, Rockville, MD 20892-7242, USA. wanderso@mail.nih.gov
Matsuno
Rayna K
RK
Sherman
Mark E
ME
Lissowska
Jolanta
J
Gail
Mitchell H
MH
Brinton
Louise A
LA
Yang
Xiaohong Rose
XR
Peplonska
Beata
B
Chen
Bingshu E
BE
Rosenberg
Philip S
PS
Chatterjee
Nilanjan
N
Szeszenia-Dabrowska
Neonila
N
Bardin-Mikolajczak
Alicja
A
Zatonski
Witold
W
Devesa
Susan S
SS
García-Closas
Montserrat
M
D000328:Adult; D000367:Age Factors; D000368:Aged; D015992:Body Mass Index; D001943:Breast Neoplasms / Q000453:epidemiology*; D016022:Case-Control Studies; D005260:Female; D020249:Hormone Replacement Therapy / Q000706:statistics & numerical data; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D009043:Motor Activity; D011044:Poland / Q000453:epidemiology; D012306:Risk; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors