A novel polypeptide wherein a part of a DCTN1 protein is fused with a part of a RET protein; a polynucleotide encoding the polypeptide; a method for detecting the polynucleotide or the polypeptide; a method for screening a compound which inhibits the expression of the polynucleotide or the expression and/or activity of the polypeptide; and a medicinal composition which comprises as an active ingredient a compound inhibiting RET.