Figure 1: Flow-chart of establishment of patient-derived xenografts. Fragments of primary tumor samples are initially implanted subcutaneously in both flanks of 1-2 immunocompromised mice, depending on tissue availability ( 𝑝 0 ). When tumors reach the exponential growth phase they are removed from donor mice, reduced into fragments, and serially transplanted in new recipient mice ( 𝑝 1 ). For investigational purposes (i.e., drug treatments or subpopulation analysis) PDXs can be expanded in a higher number of mice in order to obtain statistical relevant results or sufficient biological material for analysis, respectively. ( 𝑝 : sequential passage in immunocompromised mouse; 𝑛 : number of mice.)