Provided are a novel polypeptide wherein a portion of DCTN1 protein is fused to a portion of RET protein; a polynucleotide encoding the polypeptide; a method for detecting the polynucleotide or the polypeptide; a method of screening for a compound that inhibits expression of the polynucleotide or expression and/or activity of the polypeptide; and a pharmaceutical composition containing a compound that inhibits RET as an active ingredient.