The present invention provides an antibody that targets a cancer antigen protein that is specifically expressed on the surface of a cancer cell, and the use of the antibody as an agent for the treatment and/or prophylaxis of cancer. More specifically, the present invention provides: an antibody, or a fragment thereof, that has immunological reactivity with a CAPRIN-1 partial polypeptide comprising an amino acid sequence represented by SEQ ID NO: 5 or an amino acid sequence having greater than or equal to 80% sequence identity with said amino acid sequence； and a pharmaceutical composition for the treatment and/or prophylaxis of cancer, the pharmaceutical composition being characterized by containing the aforementioned antibody or fragment as an active ingredient.
