The present invention relates to a method for treating a tumor with a KRAS mutation. In the method, a compound 2-fluoro-5-methoxy-4-[(4-(2-methyl-3-oxo-2,3-dihydro-1H-isoindole-4-oxy)-5-trifluoromethyl-pyrimidine-2-yl)amino]-N-(1-methyl-piperidine-4-yl)benzamide or a pharmaceutically acceptable salt thereof is used, which can be administered alone or in combination with a KRAS inhibitor and/or an MEK inhibitor.