Population attributable fraction of reproductive factors in triple negative breast cancer by race.

10522 Background: Age-adjusted incidence rates of triple negative breast cancer (TNBC) are higher in African American (AA) women than in non-Hispanic White (White) women. The disproportionate incidence of TNBC in AA women partially drives the 40% higher mortality rate from breast cancer in AA women compared to White women. Several studies have identified lack of breastfeeding and younger age at first birth as risk factors for TNBC. There are large differences in breastfeeding uptake and duration in the US: only 44% of AA women breastfeed for 6 months or longer, compared to 60% of White women. To quantify the contribution of differences in breastfeeding patterns and younger age at first birth to disparities in incidence of TNBC, we calculate the population-attributable fraction (PAF), which is the proportion of the incidence of a disease that may be attributable to a particular exposure. Methods: A systematic review was performed to identify relevant case-control studies. Pooled odds ratios (ORs) for breastfeeding for < 6 months and age at first birth < 25 years were calculated from data extracted from studies using a common effect model. PAF was calculated using the Levin formula. Risk factor population prevalences were extracted from national surveys. Pooled ORs were used as estimates of relative risk (RR). A combined PAF was calculated using the polychoric correlation coefficient between breastfeeding duration and age at first birth to account for contributions of multiple risk factors. Results: Using race specific ORs, the PAF of breastfeeding for < 6 months was 12% (95% confidence interval (CI) 5-20%) among White women and 15% (95% CI 3-26%) among AA women. The PAF of having a child before age 25 was not significantly different from zero for White women (2% (CI -6-11%)) but was significantly different from zero for AA women (21% (CI 5-25%)). The combined PAF was 27% for AA women and 17% for all women in the US. Extrapolating to the US population, we estimated that 4,850 annual cases of TNBC (2,421 among White women and 1,533 among AA women) could be attributed to breastfeeding for < 6 months and age at first birth < 25 years. Conclusions: Given the protective role of breastfeeding against TNBC, policy changes aimed at supporting breastfeeding, addressing structural barriers, and promoting a culture shift could reduce racial disparities in TNBC incidence in the US. Table: see text