Research on biomedical applications of nanoparticles has seen an upsurge in recent years due to their unique capabilities in treatment of ailments. Considerable effort goes into incorporating both diagnostic and therapeutic functions into a single nanoscale system for the more effective treatment of breast cancer. Nanoparticles have great potential to achieve such dual functions, particularly if more than one type of nanostructure can be incorporated in a nanoassembly, referred to in this review as a hybrid nanoparticle. There are various types of hybrid nanostructures, such as liposomal, micellar, porous silica, polymeric, noble metal, and nanotube, which are currently used for designing theranostic nanoparticle for breast cancer. We highlight the design factors that should be considered to obtain effective nanodevices for cancer detection and treatment.