It is intended to identify a cancer antigenic protein specifically expressedon the surfaceof cancer cells and to provide an antibody targeting the antigenic protein anduse of theantibody as a therapeutic and/or preventive agent for cancer. The presentinvention providesan antibody or a fragment thereof which has immunological reactivity with aCAPRIN-1protein, the antibody comprising a heavy chain variable region comprisingamino acidsequences of SEQ ID NOs: 5. 6, and 7 and a light chain variable regioncomprising amino acidsequences of SEQ ID NOs: 9, 10, and 11, and a pharmaceutical composition fortreatmentand/or prevention of cancer, comprising this antibody or fragment as an activeingredient.
