All patients involved in this study received first-line chemotherapy regimens, which were FOLFOX and XELOX in 420 cases...The patients resistant to first-line chemotherapy showed higher percentage of PIK3CA mutation than those effective...elevated disease-progression rate in the patients with PIK3CA mutant tumors than whole cohort (24.38%, p = 0.003, Fig. 1b), which indicated a poor chemotherapy response in PIK3CA mutant CRC.