In order to establish a PDX model of CRC liver metastatic colonization, a small sample of CRC tissue, taken either from a primary or metastatic site, was dissociated and injected subcutaneously into the flanks of NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (Nod-Scid-Gamma; NSG) mice within 2 hr of surgical resection at MSKCC. The gene discussed is CTSG; the disease is colorectal carcinoma.