Abstract: Adipocytic tumors are the most common type of soft tissue tumors, which can be divided into lipomas and liposarcomas. Studies have found that benign lipomas resected from the same site can transform into liposarcomas,especially atypical lipomatous tumors(ALT), suggesting an underlying biological association. In this case, the patient underwent resection of a right neck mass in our hospital in 2017, and the pathology showed fibrolipoma. One year later, the mass recurred at the original site but was not treated. By 2023, the mass had significantly enlarged and extended deeply. MRI showed that the lesion had an unclear boundary with the surrounding fat, suggesting liposarcoma. Puncture and molecular pathology showed MDM2 gene amplification, and the diagnosis of ALT was made, which was confirmed by pathology after complete surgical resection. It can be seen that adipocytic tumors have great differences in biological behavior, and benign lipomas can transform into liposarcomas (especially ALT). Clinically, it is necessary to combine imaging, pathology and molecular detection (such as MDM2/CDK4) for differentiation to formulate treatment plans.

Key words: atypical lipomatous tumor, lipoma, liposarcoma