304 PLX4720 and Preclinical Thyroid Cancer Models Figure 4. Tumor growth and lung metastasis in an orthotopic mouse model of human anaplastic thyroid cancer. (A): Three weeks of PLX4720 treatment resulted in lower orthotopic tumor growth than in controls (***p .001). Gross photo (B1) and 3D CT scan (B3) show a large B-RafV600E 8505c orthotopic thyroid carcinoma (control, arrow) and a dramatically smaller (B2 and B4) or- thotopic tumor size with PLX4720 treatment (gross photo, arrow; 3D CT scans, asterisk) in SCID mice. (B5): Lung metastases (arrows) by GFP in control B-RafV600E 8505c orthotopic thyroid carcinoma SCID mice. (B6): Significantly fewer lung metastases in PLX4720-treated mice. (C) Control mice became cachectic between 28 and 35 days and lost an average of 23% of their baseline weight, whereas PLX4720-treated mice maintained their baseline weight (***p .001). (D): Low proliferative index (percentage of Ki-67 protein nuclear expression) in PLX4720-treated B-RafV600E 8505c orthotopic tumors, compared with controls (**p .01). Abbreviations: 3D, three-dimensional; CT, computed tomography; DMSO, dimethyl sulfoxide; GFP, green fluorescent pro- tein; SCID, severe combined immunodeficient. Tg, TSH receptor, and hNIS showed very low mRNA copy numbers ( 0.2 copy number) and no upregulation with PLX4720 treatment in 8505c cells; this result was also con- firmed by IHC, which showed undetectable protein levels both in controls and in PLX4720-treated orthotopic thyroid carcinomas.