PIK3CA and rectal cancer: Among patients with HER2-amplified CRC, the incidence of KRAS, NRAS, and PIK3CA mutations was 21.8% (19/87) (27.9% [17/61] in colon cancer, 7.7% [2/26] in rectal cancer), 3.4% (3/87)(3.3% [2/61] in colon cancer, 3.8% [1/26] in rectal cancer), and 11.5% (10/87) (13.1% [8/61] in colon cancer, 7.7% [2/26] in rectal cancer), respectively.