The sum of baseline scan target lesion diameters is 58mm with a mean density of 89.5 HU, and the sum of current target lesion diameters is 80.9mm  with a mean density of 88.0 HU thus the change in tumor size is 39.5 % with -1.7 % change of tumor density indicating progressive extra-intestinal GIST according to Choi Response Criteria

Primary GISTs could affect the peritoneum involving the mesentery or omentum. It appears heterogeneous due to internal hemorrhage, necrosis, and cystic change; the solid component enhances upon contrast administration. It may be indistinguishable from malignant fibrous histiocytoma, leiomyosarcoma, liposarcoma, and other sarcomas including metastasizing GISTs from the gastrointestinal tract on cross-sectional imaging ¹.