Sex Discordance and Risk of Breast Cancer, A Twin Study

Abstract Objective The purpose of the study is to perform an analysis of the relationship between sex discordance and risk of breast cancer in female twins in the United States. Methods A cross-sectional study of 14,462 female twins was conducted using data from Washington State Twin Registry (WSTR) in the USA. The variables collected included, BMI, age, race and zygosity. This study used Generalized Estimating Equation (GEE) modeling to determine the relationships between twin pairs and variables of interest such as breast cancer and sex concordance. Zygosity, BMI, age and race were used for adjustment. Proband wise concordance was done to ascertain the heritability of breast cancer in twins. Results Being a female-female twin pair increased the odds of breast cancer by 34% (95%CI: 1.18-1.53). After adjusting for zygosity, age, BMI, race, and childbirth, the odds of breast decreased by 31% in female-female twin pairs [AOR (95%CI):0.69 (0.53-0.90)]. The proband wise concordance was higher in monozygotic twins as compared to dizygotic twins. The values for dizygotic and monozygotic twins were 4 and 17 respectively. Conclusion The findings of the study show that there is a positive association between sex concordance and breast cancer in female twins though other factors such as zygosity, BMI and age can influence breast cancer diagnosis. From our study, the proband wise concordance for monozygotic twins was higher than that of dizygotic twins. Breast cancer is therefore considered heritable.