Estimating age-specific breast cancer risks: a descriptive tool to identify age interactions.

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.
Cancer Causes and Control (Impact Factor: 2.96). 06/2007; 18(4):439-47. DOI: 10.1007/s10552-006-0092-9
Source: PubMed

ABSTRACT Clarifying age-specific female breast cancer risks and interactions may provide important etiologic clues.
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.
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.
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.

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