The most frequently occurring mutually exclusive modules were related to the PI3K-AKT-mTOR pathway, including the mutations in ERBB2, PIK3CA, PIK3R1, PTEN, and AKT1. These molecules appeared in an exclusive reciprocal manner not only in the entire breast cancer cohort but also in the YBC and OBC subgroups as well (Additional file 2: Fig. S1A). This evidence concerns the gene PIK3R1 and breast cancer.