Abstract 3471: Total red meat, unprocessed red meat, processed meat and risk of breast cancer - a pooled analysis of 23 cohort studies
Authors: Wu You , Willett Walter C. , Smith-Warner Stephanie A. 
Published: September 2020

Abstract
Background: The relationship between red meat consumption and breast cancer has been evaluated in several epidemiological studies, yet there has been no clear scientific consensus. Further, few studies have comprehensively investigated the effect of substituting other major protein sources for red meat on the risk of breast cancer. Thus, we combined data from large cohort studies to examine the associations between total red meat, unprocessed red meat, and processed meat intake and breast cancer risk, as well as the effects of substituting alternative protein sources for red and processed meat on breast cancer risk.
Methods: This study included 23 prospective cohort studies with over 1 million women among whom 46,176 (28,870 estrogen receptor (ER) positive; 6,354 ER negative) breast cancer cases were diagnosed during follow-up. Using harmonized participant-level data, study-specific hazard ratios (HR) and 95% confidence intervals (CI) were calculated using Cox proportional hazards regression. Consumption of each protein source was analyzed as calories consumed per day and the various sources were modeled as continuous variables simultaneously in multivariable-adjusted models. The difference in beta coefficients between two protein sources was used to estimate substitution effects. The study-specific estimates were pooled using a random-effects model.
Results: Median consumption of total red meat (63 - 336 kcal/day), unprocessed red meat (42 - 300 kcal/day), and processed meat (11 - 90 kcal/day) varied substantially across studies. Total red meat, unprocessed red meat, and processed meat intakes were not significantly associated with risk of breast cancer when holding intake of other protein sources constant. Significant inverse associations were observed when substituting 200kcal/day of red meat with an energy-equivalent amount of mature beans (legumes) (pooled HR = 0.92, 95%CI: 0.87-0.98) and dairy products (pooled HR = 0.96 (95% CI: 0.94-0.99). There were no statistically significant substitution effects for chicken, seafood, and nuts. Results were similar for unprocessed red meat. For processed meat, the substitution effects were generally in the same direction, but weaker due to use of a lower increment (50kcal/day, an amount more representative of the quantity of processed meat consumed in these studies). However, a marginally significant higher risk of breast cancer was observed when substituting egg intake for processed meat (pooled HR = 1.10, 95% CI: 1.00-1.21). No significant differences in any of these associations were observed between the ER subtypes.
Conclusions: Although we found that total red meat and unprocessed red meat were not associated with breast cancer risk, substituting their consumption with mature beans or dairy products was associated with a significantly lower risk of breast cancer. No significant associations were shown for processed meat.
Citation Format: You Wu, Walter C. Willett, Stephanie A. Smith-Warner. Total red meat, unprocessed red meat, processed meat and risk of breast cancer - a pooled analysis of 23 cohort studies [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3471.