Reproductive factors and risk of breast cancer by tumor subtypes among Ghanaian women: A population-based case–control study
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Date
2020-02-18
Journal Title
Journal ISSN
Volume Title
Publisher
International Journal of Cancer
Abstract
Higher proportions of early-onset and estrogen receptor (ER) negative cancers are observed in women of African ancestry than
in women of European ancestry. Differences in risk factor distributions and associations by age at diagnosis and ER status may
explain this disparity. We analyzed data from 1,126 cases (aged 18–74 years) with invasive breast cancer and 2,106 controls
recruited from a population-based case–control study in Ghana. Odds ratios (OR) and 95% confidence intervals (CI) were
estimated for menstrual and reproductive factors using polytomous logistic regression models adjusted for potential
confounders. Among controls, medians for age at menarche, parity, age at first birth, and breastfeeding/pregnancy were
15 years, 4 births, 20 years and 18 months, respectively. For women ≥50 years, parity and extended breastfeeding were
associated with decreased risks: >5 births vs. nulliparous, OR 0.40 (95% CI 0.20–0.83) and 0.71 (95% CI 0.51–0.98) for ≥19 vs.
<13 breastfeeding months/pregnancy, which did not differ by ER. In contrast, for earlier onset cases (<50 years) parity was
associated with increased risk for ER-negative tumors (p-heterogeneity by ER = 0.02), which was offset by extended
breastfeeding. Similar associations were observed by intrinsic-like subtypes. Less consistent relationships were observed with
ages at menarche and first birth. Reproductive risk factor distributions are different from European populations but exhibited
etiologic heterogeneity by age at diagnosis and ER status similar to other populations. Differences in reproductive patterns and
subtype heterogeneity are consistent with racial disparities in subtype distributions.
Description
Research Article
Keywords
reproductive risk factors, subtype heterogeneity, racial disparities, breast cancer