An object of the present invention is to provide a novel tumor marker and use thereof. In more detail, the present invention provides a novel tumor marker, a method for measuring said tumor marker and a measurement kit, a method for detecting cancer using the same, a kit for detecting cancer, a method for screening a preventive and/or therapeutic agent for cancer, as well as a medicament such as cancer vaccine. According to the present invention, a method for measuring an alternative splicing variant of OATPIB3 mRNA in a sample to be examined is provided. Said measurement method comprises measuring mRNA comprising a nucleotide sequence represented by SEQ ID NO: 1 in the sequence listing table in a sample to be examined isolated from living organism with differentiation from a mRNA comprising a nucleotide sequence represented by SEQ ID NO: 2. Said measurement method is useful for detecting cancer or screening a preventive and/or therapeutic agent.
