The present invention relates to an isolated domain of G3BP-2 that mediates binding between G3BP-2 and other proteins, and nucleic acids encoding same. The invention also relates to a method for diagnosing, treating and preventing breast cancer including the step of using a nucleic acid and/or encoded polypeptide for G3BP-2, or fragment thereof, to detect, treat or prevent breast cancer in a mammal, preferably human. In one particular form, the invention relates to an antigen presenting cell, preferably a dendritic cell, that is capable of presenting G3BP-2 or fragments thereof. The invention also relates to lymphocytes, in particular cytotoxic T-lymphocytes, that are G3BP-2 antigen specific.