NRAS and digestive system neoplasm: The frequencies of mutations in KRAS, BRAF, PIK3CA and NRAS were compared with previous researches, the KRAS and BRAF mutation frequencies were close to early studies11, 12, 18, 41, however, data based on another population presented lower KRAS and BRAFmutants10, more sigmoid and rectum tumors involved in their cohort may contribute to the lower mutation frequency.