Abstract: Provided is a lung adenocarcinoma detection method that is simple and is less invasive. The lung adenocarcinoma detection method of the present invention includes the step of detecting the presence or absence of an abnormal cleavage in kininogen I in a sample collected from a subject in vitro. The abnormal cleavage in kininogen I is, for example, a cleavage that can form at least one cleaved site in a peptide bond in kininogen I and/or a cleavage that causes the deletion of at least one amino acid residue at least one site in kininogen I. The lung adenocarcinoma detection method according to the present invention includes the step of detecting the presence or amount of a protein having the above-mentioned abnormal cleavage or the loss of the amount of a normal protein, and the like.