Case Report: Recurrent retroperitoneal dedifferentiated liposarcoma after surgery.

Objective: This study aims to summarize a comprehensive therapeutic strategy for recurrent retroperitoneal dedifferentiated liposarcoma (DDLPS) and evaluate the potential value of combining targeted therapy with radiotherapy. Methods: We retrospectively reviewed the complete clinical course of a patient with recurrent retroperitoneal DDLPS, focusing on recurrence patterns following the initial R0 resection, secondary surgical management, molecular testing findings, targeted therapy, radiotherapy, and follow-up outcomes. Additionally, a relevant literature review was conducted to support the analysis. Results: The first recurrence, measuring 1.3 cm, occurred 21 months after the initial operation, with the lesion enlarging to 4.7 cm by month 28, leading to a second laparoscopic resection. A second recurrence was noted 3 months postoperatively. Based on MDM2/CDK4 amplification, abemaciclib was administered at a dosage of 150 mg twice daily, resulting in stable disease with less than 20% tumor growth. Radiotherapy (50 Gy/25 fractions) was subsequently added after 2 months of targeted therapy, leading to tumor shrinkage to 4.8 cm × 3.1 cm (a 21.3% reduction in longest diameter) and a marked reduction in solid components. Per RECIST 1.1 criteria, the best overall response was stable disease (SD), although the reduction in tumor density suggested a clinically favorable response. Conclusions: Retroperitoneal DDLPS is characterized by a high recurrence rate. Complete surgical resection remains the cornerstone of treatment for localized disease. In recurrent cases, CDK4/6 inhibition guided by molecular profiling may provide effective disease control, and the addition of radiotherapy after targeted therapy appeared to confer an additive benefit in this patient. However, these findings are hypothesis-generating and require validation in future prospective studies.