There is provided a simple and minimally invasive adenocarcinoma detection method. The adenocarcinoma detection method of the present invention includes a step of detecting in vitro a presence or absence of an abnormal cleavage in a specific protein in a test subject-derived sample. The abnormal cleavage in the specific protein is, for example, a cleavage resulting in one or more breaks in a peptide bond in the specific protein and/or a cleavage resulting in a deletion of one or two more amino acid residues at one or more sites of the specific protein. The adenocarcinoma detection method of the present invention includes a step of detecting a presence or amount of a protein having the abnormal cleavage or a decrease in an amount of a normal protein.