Disclosed are a novel method of detecting cancer, a method of screening inhibitors and anticancer agents that target cancer-related molecules, RHOA polypeptide having mutation and a polynucleotide encoding the polypeptide as a therapeutic agent for cancer, and a method of detecting cancer using the polypeptide or polynucleotide. Also disclosed are a vector and a host cell comprising the polynucleotide, a method of screening therapeutic agents for cancer comprising the polypeptide and/or the polynucleotide, and a therapeutic agent for cancer comprising siRNA having a silencing effect on RHOA mutant.