The present invention makes it possible to obtain a novel therapeutic drug for malignant tumors. Specifically, the present invention provides a therapeutic drug for malignant tumors, said drug including an anti-LSR (lipolysis stimulated lipoprotein receptor) antibody or an antigen-binding fragment thereof, or a functional equivalent thereof, or an LSR inhibitor such as a nucleic acid. Said inhibitor uses a therapeutic drug for malignant tumors, said drug including an anti-LSR antibody, or an antigen-binding fragment thereof or a functional equivalent thereof. The inhibitor may also be an LSR antagonist. The abovementioned therapeutic drug may be administered to patients in whom the onset of an LSR-positive malignant tumor is judged to have occurred.
