The present invention identifies a cancer antigen protein which is expressed specifically on the surface of a cancer cell, and provides a use of an antibody, which targets the cancer antigen protein, as a therapeutic and/or prophylactic agent for cancer. Specifically disclosed is a pharmaceutical composition for the treatment and/or prevention of cancer, which is characterized by containing, as an active ingredient, an antibody that is immunologically reactive with a partial polypeptide of CAPRIN 1 represented by the even- numbered sequences of SEQ ID NOS: 2-30, said partial polypeptide comprising the amino acid sequence represented by SEQ ID NO: 37 or an amino acid sequence having 80% or more sequence identity to the amino acid sequence, or a fragment of the antibody.
