This chapter discusses alternative routes of tumor development, either for a short-term drug screening assay or because the tumor type studied not be accepted by any route except the brain. Fresh tumor implants from surgical specimens, as well as fragments from human tumor xenografts, were analyzed upon subrenal capsule (SRC) implantation, either as control tumors or after treatment. A number of investigators have analyzed the SRC assay of first transplant generation tumors in normal mice for its predictive value for drugs to be active in a particular tumor type or even in an individual patient. Cell cultures of such tumor types were reported to have preferential growth in immunologically privileged sites, such as the brain. Tumor systems have been made available in which tumor cells are injected into the brain and treatment is instituted on designated schedules following the inoculation of the tumor cells.