Number of children and risk of hormone receptor-positive versus hormone receptor-negative breast cancer

Abstract

Introduction: With around 2.3 million cases, breast cancer became the most frequently diagnosed cancer in 2020 surpassing lung cancer cases and mortality. Based on histology and molecular characteristics, hormone receptor-positive (HR+) cancer has tumors with both estrogen and progesterone receptors. On the contrary, hormone receptor-negative (HR-) cancer has tumors not expressing estrogen or progesterone receptors. Getting pregnant before age of 30 years reduced the probability of disease by 50% compared to women who were childless. Material and Methods: Data from the Norwegian Women and Cancer (NOWAC) cohort study from 1991 to 2018 was used. Based on the DAG diagram, our final survival model included the age of participants at the start of the study, their age at menarche, height, and the use of oral contraceptives. The Cox proportional hazards method was used to determine the effect of the number of children diagnosed with HR+ or HR- breast cancer. All demographic and lifestyle variables were compared with the number of children, breast cancer, and non-cases using the Chi-square test and one-way ANOVA test in the two descriptive tables. Results: The multivariable analysis showed that multiparous women had a 26% lower risk of breast cancer (HR= 0.74, 95% CI: 0.65-0.85) while women with one or two children also had a 12 % reduced risk of breast cancer compared to the reference group (HR= 0.88, 95% CI: 0.78-1.01). The multivariable analysis of HR+ breast cancer showed women with multiple children had 34% lower risk (HR=0.66, 95% CI: 0.57-0.76) and women with one or two children had 16% decreased risk of HR+ breast cancer (HR=0.84, 95% CI: 0.72 - 0.96) compared to nulliparous women. Moreover, the multivariable analysis comparing with the reference group showed a greater risk of HR- breast cancer by 24% among women having multiple children (HR=1.24, 95% CI: 0.70 - 2.17) while women with fewer children had a 25 % greater risk of HR- breast cancer (HR=1.25, 95% CI: 0.72 -2.19). Conclusion: In conclusion, having children was associated with a lower risk of breast cancer overall and hormone receptor-positive breast cancer diagnosis in Norwegian women. On the contrary, we have not observed the same association between the number of children and the risk of hormone receptor-negative breast cancer.