PPP1R21 and breast cancer: Interestingly, the at-BC-risk allele C of this polymorphism determines the high expression of the PPP1R21 gene in both the mammary gland and fibroblasts, but is associated with low eQTL of all other genes in the mammary gland (GTF2A1L, RP11-460M2.1, STON1-GTF2A1L, and MSH6), fibroblasts (GTF2A1L, FOXN2, and MSH6) and liver (GTF2A1L) (Supplementary Table S4).