CCNE1 and gastric cancer: In addition, lower HER2 amplification levels,9 co‐amplification of HER3, CCNE1, EGFR or MET,10, 11, 12 and co‐alteration in the downstream RTK/RAS/RAF pathway and PI3K/AKT/mTOR pathway molecules has also been demonstrated to be associated with trastuzumab resistance in GC.