Four Cases with FUS/CHOP Fusion Gene Products Positive Myxoid Liposarcoma Responding Effectively to Trabectedin Monotherapy

Background: Myxoid liposarcoma, a rare type of tumor, accounts for approximately 30% of all liposarcomas. Myxoid liposarcomas harboring the FUS/CHOP fusion gene have shown promising results with trabectedin in basic research and some clinical experiments. However, the efficacy and safety of trabectedin in chemotherapy-naive soft tissue sarcomas or FUS/CHOP fusion gene-positive myxoid liposarcomas have not yet been established. Therefore, we evaluated the effectiveness and safety of trabectedin monotherapy in four cases of myxoid liposarcoma harboring the FUS/CHOP fusion gene at our hospital. Patients and Methods: We analyzed four patients with metastatic myxoid liposarcoma who underwent surgery at Okayama University and received chemotherapy at Kawasaki Medical School. These patients had positive test results for the FUS/CHOP fusion gene as an aid to pathological diagnosis by RT-PCR. RNA was extracted from tumor tissue sliced from frozen tumor specimens. Following reverse transcription, PCR was performed using TLS/FUS-CHOP primers. The resulting products were electrophoresed, and then the nucleotide sequences were confirmed. Case Presentation: Case 1: A 44-year-old male started trabectedin as second-line therapy after initial chemotherapy, which included doxorubicin. To date, he has completed 9 cycles, showing a response for 6 months. Case 2: A 71-year-old male, deemed intolerant to doxorubicin, started trabectedin as his first-line treatment. He has undergone 50 cycles to date, maintaining a response for 56 months. Case 3: A 59-year-old female began trabectedin as second-line therapy after initial chemotherapy, including doxorubicin. She responded for 6 months before experiencing disease progression. Case 4: A 79-year-old male developed new lesions after one course of initial chemotherapy, including doxorubicin. He then began trabectedin and has maintained a response for 10 months to date. Conclusion: Compared to other chemotherapies, trabectedin demonstrated potentially higher efficacy and a favorable safety profile for patients with myxoid liposarcoma harboring the FUS/CHOP fusion gene.