A rare case of well-differentiated liposarcoma with CDK4 amplification but without MDM2 amplification

Abstract Background: Well-differentiated liposarcoma (WDL)/atypical lipomatous tumor (ALT) and dedifferentiated liposarcoma (DDL) together comprise the largest subgroup of liposarcomas, and constitute up to 20% of all soft tissue sarcomas. WDL shares a common genetic feature characterized by high-level amplifications in the chromosome 12q13-15 region which contains the murine double minute-2 (MDM2), cyclin-dependent kinase-4 (CDK4) genes, and high mobility group protein AT-hook 2 (HMGA2). This is the first time we report a rare case of WDL with CDK4 amplification but without MDM2 amplification. Case presentation: A 61-year-old male presented with increased urine volume at night without fever, backache, abdominal distension, hematuria, urine pain, and other uncomfortable symptoms. Abdominal computed tomography revealed an uneven density, 6.6*6.3*6.1cm mass in the right renal inferior retroperitoneum. The patient was treated with the right retroperitoneal tumor resection. Light microscopy revealed a large number of necrotic areas, fibers separated into leaflets of varying size, fat-like cell sizes differences, with enlarged, deep stained, irregular nuclei, and scattered irregular spindle cells within the fiber septum. The MDM2 gene was not amplification by fluorescence in situ hybridization (FISH) which was considered the gold standard. A FISH assay with break-apart probes to detect DDIT3 gene rearrangement was negative. CDK4 gene amplification was detected by FISH. The diagnosis of the mass was WDL with CDK4 amplification but without MDM2 amplification. The patient was followed up for three months without symptoms and residual/recurrent tumors. Conclusions: WDL usually has MDM2, CDK4 gene amplification, and in some cases can have only MDM2 gene amplification without CDK4 gene amplification, but also note that this WDL with CDK4 amplification but no MDM2 amplification. Therefore, this case is of great significance to the clinical work of the pathologists.