SPHK1 and Familial prostate cancer: Herein, we further expand this theranostic small-molecule prodrug conjugate (T-SMPDC) design concept to develop a theranostic agent for NEPC-targeted delivery and controlled intracellular release of fingolimod (FTY720)—a sphingosine kinase 1 (SphK1) inhibitor—for precision therapy of prostate cancer (Figure 1).