The aim of this thesis was to explore iron oxide nanoparticles (IONPs) for ultimate detection and co-treatment of early prostate cancer (PC) lymph node metastases. IONPs previously optimized as a theranostic tool for the combined use in MRI and magnetic hyperthermia were functionalized with an RNA aptamer or a small molecule, both actively targeting the prostate-specific membrane antigen (PSMA). Functionalized IONPs were developed to meet the requirements for lymphatic targeting and specific binding to PSMA-expressing PC cells while preserving high MRI relaxivity and heating properties. In a second project, we designed and tested an in situ forming implant entrapping IONPs as a heating source for magnetic hyperthermia with intended application in localized PC. Besides appropriate syringeability and implant formation upon injection, we confirmed homogeneous intrinsic radiopacity in micro-CT in vivo. When applying magnetic field strengths and frequencies eligible for use in humans, the implant reached the hyperthermia target temperature of 48 °C.