PIK3CA and breast neoplasm: In this model, expression of the mutant protein is driven by the endogenous promoter and thus is expressed at physiological levels and only in cells that normally express Pik3ca. This model accurately reproduces the scenario of a somatic mutation in a single PIK3CA allele as occurs in human breast tumors making it ideal for both studying the role of PIK3CA mutation in tumourigenesis and for preclinical studies evaluating therapies targeting the PI3K pathway.