Personalized medicine holds tremendous promise for the treatment of heterogeneous diseases such as cancer. The ability to test treatment approaches in representative in vitro systems that mirror the individual features of a patient’s disease, has the potential to improve treatment efficacy greatly, while avoiding unnecessary side effects. Tumoroids, small tumors grown in 3D culture, are among the most promising “patient avatars” for cancer therapy. However, their routine application in therapy design is hampered by high cost and very long assay procedures. In the course of this PHRT project, we will develop and benchmark a novel, personalized tumoroid assay that can deliver detailed susceptibility and resistance profiles for prostate and bladder cancer patients within few weeks after biopsy. Routine implementation of our assay strategy will enable oncologists to maximize the initial treatment response and minimize the development of treatment resistance.