Estimating age-specific breast cancer risks: a descriptive tool to identify age interactions.
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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ABSTRACT: Breast cancer is a heterogeneous disease, divisible into a variable number of clinical subtypes. A fundamental question is how many etiological classes underlie the clinical spectrum of breast cancer? An etiological subtype reflects a grouping with a common set of causes, whereas a clinical subtype represents a grouping with similar prognosis and/or prediction. Herein, we review the evidence for breast cancer etiological heterogeneity. We then evaluate the etiological evidence with mRNA profiling data. A bimodal age distribution at diagnosis with peak frequencies near ages 50 and 70 years is a fundamental characteristic of breast cancer for important tumor features, clinical characteristics, risk factor profiles, and molecular subtypes. The bimodal peak frequencies at diagnosis divide breast cancer overall into a "mixture" of two main components in varying proportions in different cancer populations. The first breast cancer tends to arise early in life with modal age-at-diagnosis near 50 years and generally behaves aggressively. The second breast cancer occurs later in life with modal age near 70 years and usually portends a more indolent clinical course. These epidemiological and molecular data are consistent with a two-component mixture model and compatible with a hierarchal view of breast cancers arising from two main cell types of origin. Notwithstanding the potential added value of more detailed categorizations for personalized breast cancer treatment, we suggest that the development of better criteria to identify the two proposed etiologic classes would advance breast cancer research and prevention.JNCI Journal of the National Cancer Institute 08/2014; 106(8). DOI:10.1093/jnci/dju165 · 15.16 Impact Factor
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ABSTRACT: We examined the relationship between reproductive factors and risk of premenopausal breast cancer among women less than age 40 compared with older premenopausal women. We documented 374 incident cases of breast cancer diagnosed before age 40, and 2,533 cases diagnosed at age 40 and older among premenopausal women in the Nurses' Health Study cohorts. Biennial questionnaires were used to determine age at menarche, age at first birth, parity, breastfeeding, and other reproductive factors. Multivariate relative risks (RR) and 95 % confidence intervals (CI) were calculated using Cox proportional hazards models within age at diagnosis groups. Tumors in younger women were significantly more likely to be higher grade, larger size, and hormone receptor negative than were tumors in older premenopausal women (p < 0.0001). There was no significant heterogeneity according to age in associations between reproductive factors and risk of premenopausal breast cancer. First birth at age 30 or older increased breast cancer risk in both age groups (age <40: RR 1.10, 95 % CI 0.80-1.50; age ≥40: RR 1.16, 95 % CI 1.02-1.32; p-heterogeneity = 0.44). Risk of premenopausal breast cancer decreased with each additional year of age at menarche in both age groups (age <40: RR 0.93, 95 % CI 0.87-0.99; p trend = 0.02; age ≥40: RR 0.94, 95 % CI 0.91-0.97; p trend = <0.0001). Among premenopausal parous women, breastfeeding was protective regardless of age at diagnosis (age <40: RR 0.84, 95 % CI 0.57-1.22; age ≥40: RR 0.85, 95 % CI 0.72-0.99; p-heterogeneity = 0.79). In the largest prospective examination of reproductive risk factors and risk of breast cancer before and after age 40, we found that younger women were more likely to develop tumors with less favorable prognostic characteristics. However, associations between reproductive factors and risk of breast cancer were similar regardless of age at diagnosis of premenopausal breast cancer.Breast Cancer Research and Treatment 10/2013; DOI:10.1007/s10549-013-2721-9 · 4.20 Impact Factor