When our composite included all-cause mortality, surrogate endpoints for overall survival as well as non-fatal breast cancer events (17 studies, >1,088 events in 9,555 participants), individuals with any copy of a reduced function CYP2D6 allele had a RR of achieving this end point of 1.19 (95% CI: 1.07 to 1.33; I2=53%) for fixed effects and 1.22 (95% CI: 1.01 to 1.46) for random effects meta-analysis compared to those with normal or increased function CYP2D6 alleles (Figure 1, Table S6 and Figure S8). Here, CYP2D6 is linked to breast cancer.