PIK3CA and breast cancer: This pathway also emerges as pivotal in our results: indeed, the most common STPs in breast cancer are PIK3CA ⇒ S100B and PIK3CA ⇒ MMP13 (see Table 1); PIK3CA is one of only three core source genes appearing in at least three tissues (see Fig 3); and in breast cancer, PIK3CA is virtually certain to have a downstream RNA aberrant target (see Table L in S1 Text).