PMC4578851_01
At low power (a, b, x100), the metastatic GIST resected in 2014 demonstrated variable cellularity, with spindled to predominately epithelioid cells embedded within a myxoid stroma. On high power (c, x400) cellular areas demonstrated sheets of epithelioid tumor cells with abundant cytoplasm and monotonous nuclei with finely granular chromatin, typical for epithelioid GIST. Scattered mitotic figures were present. Immunohistochemical study for DOG1 (d, x200) was diffusely positive in tumor cells
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Fig1
All three lesions were excised and consistent with metastatic GIST (Fig. 1).
PET/CT imaging prior to (a-d) and after 10 weeks (e-h) of sunitinib therapy. Prior to treatment, whole body PET (a) revealed a large hypermetabolic lesion in the dome of the liver, a PET-avid sub-cm L hepatic lesion, and hypermetabolic activity in the abdominal wall near the site of previous surgical resection. On cross sectional CT imaging (b) the large hepatic lesion measured 5.9 x 5.1 cm in maximal dimension, and the corresponding area on PET imaging (c) and fused PET/CT (d) revealed an SUVmax of 8.4. Both liver lesions were no longer detectable on repeat imaging (e-h), and the surgical site hypermetabolic activity decreased (e), consistent with resolving post-operative changes
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Fig2
On first restaging imaging after 10 weeks of treatment, PET/CT imaging revealed a dramatic improvement with the large hypermetabolic liver lesion no longer visible, nor was visible the smaller hepatic focus of FDG uptake (Fig. 2).