By using an antisense nucleotide, a ribozyme, a maxizyme, or an RNAi constructed based on the nucleotide sequence of exon 1 beta of the PDGF receptor alpha gene, which is expressed in specific cancer cells, or a polypeptide containing a portion thereof, translation of an mRNA transcribed from exon 1 beta of the PDGF receptor alpha gene is suppressed. An agent for suppressing expression containing as an active ingredient a substance for inhibiting expression, such as an antisense nucleotide, a ribozyme, a maxizyme, or an RNAi, is effective as a therapeutic agent for cancer.