Abstract
ObjectivesThe relationship between reproductive factors and breast cancer (BC) risk has been investigated in previous studies. Considering the discrepancies in the results, the aim of this study was to estimate the causal effect of reproductive factors on BC risk in a case-control study using the double robust approach of targeted maximum likelihood estimation.MethodsThis is a causal reanalysis of a case-control study done between 2005 and 2008 in Shiraz, Iran, in which 787 confirmed BC cases and 928 controls were enrolled. Targeted maximum likelihood estimation along with super Learner were used to analyze the data, and risk ratio (RR), risk difference (RD), andpopulation attributable fraction (PAF) were reported.ResultsOur findings did not support parity and age at the first pregnancy as risk factors for BC. The risk of BC was higher among postmenopausal women (RR = 3.3, 95% confidence interval (CI) = (2.3, 4.6)), women with the age at first marriage ≥20 years (RR = 1.6, 95% CI = (1.3, 2.1)), and the history of oral contraceptive (OC) use (RR = 1.6, 95% CI = (1.3, 2.1)) or breastfeeding duration ≤60 months (RR = 1.8, 95% CI = (1.3, 2.5)). The PAF for menopause status, breastfeeding duration, and OC use were 40.3% (95% CI = 39.5, 40.6), 27.3% (95% CI = 23.1, 30.8) and 24.4% (95% CI = 10.5, 35.5), respectively.ConclusionsPostmenopausal women, and women with a higher age at first marriage, shorter duration of breastfeeding, and history of OC use are at the higher risk of BC.
Highlights
In previous decades, most cases of cancer have occurred in more developed countries, but recently the pattern has shifted towards developing or less-developed countries; these countries account for about 82% of the world’s population, with about 57% of cancer cases and 65% of deaths from cancer [1]
Postmenopausal women, women with higher age at marriage, women with lower breastfeeding duration, and women with a history of oral contraceptive (OC) usage are at greater risk of Breast Cancer (BC)
Encouraging people to marry at a younger age, and increasing breastfeeding duration, as well as policies to reduce the use of hormonal contraceptives, can be effective in reducing BC cases
Summary
Most cases of cancer have occurred in more developed countries, but recently the pattern has shifted towards developing or less-developed countries; these countries account for about 82% of the world’s population, with about 57% of cancer cases and 65% of deaths from cancer [1]. Breast Cancer (BC) has the highest number of incident cases [3]; it alone accounts for 25% of cancer cases and 15% of cancer deaths among women, with almost half of the new cases and 38% of deaths occurring in more developed countries [1, 4]. It has the highest annual incidence among women in 161 countries and is the leading cause of cancer death in 98 countries [5]. The incidence and deaths from BC have increased in Asian countries including Iran [1, 3, 6]
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