It is of note, however, that the generally poor prognosis of patients with the combination of both PTEN deletion and HER2 amplification as determined in a historical breast cancer patient set predating the era of anti-HER2 therapies demonstrates that the poor success of trastuzumab in PTEN deleted cancers may also be driven by increased cancer aggressiveness irrespective of therapy response. This evidence concerns the gene PTEN and breast cancer.