PIK3CA and breast cancer: Based on these constructed oncogenetic tree models, some common findings are revealed as the following inferences: (a) ErbB2 is close to the root of the tree, indicating that its alteration is potentially an early event in breast cancers; (b) at least three subtrees appear to follow up the event of ErbB2, which indicates that there are pathways of progression in human breast cancer; (c) a close relationship is revealed between KRAS and PIK3CA alterations, since they are consistently grouped to the same subcluster.