Since in breast cancer patients it has been demonstrated that PTEN loss of expression confers resistance to trastuzumab (a monoclonal antibody, MoAb, against Her-2, a tyrosine kinase receptor belonging to the Her family, as EGFR) (43), recent reports have investigated whether PTEN alterations may affect responsiveness of mCRC patients to anti-EGFR MoAbs cetuximab and panitumumab (Table 3). This evidence concerns the gene EGFR and breast cancer.