(P 387) SUCCESSFUL PAZOPANIB TREATMENT OF UNDIFFERENTIATED PLEOMORPHIC SARCOMA WITH COAMPLIFICATION OF PDGFRA, VEGFR2, AND KIT: A CASE REPORT

Objective: The genetic characteristics of patients with soft tissue sarcomas (STSs) who respond to pazopanib are not well understood. Patients with undifferentiated pleomorphic sarcoma (UPS) that recurs or metastasizes generally have a poor prognosis. We report a case of a patient with advanced UPS, characterized by coamplification of the PDGFRA, VEGFR2, and KIT genes, who experienced a prolonged and complete response to pazopanib. This case suggests that coamplification of these genes may predict positive outcomes with pazopanib treatment.

Methods: A 51-year-old man presented with abdominal pain and swelling and pain in his left thigh. A CT scan revealed unexplained intra-abdominal bleeding near the pancreatic head. MRI showed a tumor in the left thigh's femoral bone with bleeding and bone destruction. PET/CT detected increased metabolic activity in a retroperitoneal tumor, as well as tumors in the pancreatic head lymph nodes, second and fifth thoracic vertebrae, and left femoral bone. Based on the morphology, immune profile, and clinical presentation, the patient was diagnosed with UPS originating in the retroperitoneum, with metastases to the bones and lymph nodes.

Results: The patient received denosumab and radiation therapy (35 Gy in 5 fractions) to the left femur and second and fifth thoracic vertebrae, followed by 75 mg/m² doxorubicin on day 1 of a 21-day cycle for 8 cycles. After chemotherapy, the primary retroperitoneal lesion and bone metastases shrank, and no new lesions appeared, indicating a partial response (PR). A comprehensive genomic profiling test was conducted to determine second-line chemotherapy, revealing coamplification of the PDGFRA, VEGFR2, and KIT genes. Pazopanib was then administered as the second-line treatment.
Remarkably, the primary retroperitoneal tumor further reduced in size, and no new lesions developed for three years after starting pazopanib, indicating a complete response (CR).

Conclusion: This case suggests that although STSs with amplified PDGFRA, VEGFR2, and KIT are rare, patients with these genetic features may benefit from pazopanib therapy. A limitation of this study was the lack of immunohistological analysis for markers such as PDGFRA, VEGFR2, KIT, VEGF, and PDGF. Further studies are needed to confirm the benefits of pazopanib in patients with the coamplification and to establish predictive markers for pazopanib sensitivity.