Causal effect of sarcopenia-related traits on the occurrence and prognosis of breast cancer - A bidirectional and multivariable Mendelian randomization study

Background and aims: although sarcopenia is associated with several types of cancer, there is limited research regarding its effect on breast cancer. We aimed to explore the causality between sarcopenia-related traits and the incidence and prognosis of breast cancer. Methods: two-sample bidirectional and multivariate Mendelian randomization (MR) analyses were utilized in this study. Genome-wide association studies were used to genetically identify sarcopenia-related traits, such as appendicular lean mass, grip strength of both hands, and walking pace. Data on the incidence and prognosis of breast cancer were collected from two extensive cohort studies. Multivariate MR analysis was used to adjust for body mass index, waist circumference, and whole-body fat mass. The primary method used for analysis was inverse-variance weighted analysis. Results: a significant association was found between appendicular lean mass and ER- breast cancer (OR = 0.873, 95 % CI: 0.817-0.933, p = 6.570 × 10-5). Increased grip strength of the left hand was associated with a reduced risk of ER- breast cancer (OR = 0.744, 95 % CI: 0.579-0.958, p = 0.022). Stronger grip strength of the right hand was associated with prolonged survival time of ER+ breast cancer patients (OR = 0.463, 95 % CI: 0.242-0.882, p = 0.019). In the multivariable MR analysis, appendicular lean mass, grip strength of both hands, and walking pace were still genetically associated with the development of total breast cancer and ER-/+ breast cancer. Conclusions: several sarcopenia-related traits were genetically associated with the occurrence and prognosis of breast cancer. It is crucial for elderly women to increase their strength and muscle mass to help prevent breast cancer.