Dedifferentiated liposarcoma with extensive cystic change causing significant diagnostic challenges: report of two cases and review of the literature.

Background: Retroperitoneal dedifferentiated liposarcoma is a rare, aggressive malignancy, characterized by high rates of recurrences and the potential for metastasis. On imaging, these tumors typically present as a solid mass with lipomatous and non-lipomatous components. Cystic changes of dedifferentiated liposarcomas is exceedingly rare and might pose significant diagnostic challenges, with only a few cases reported in the literature. REPORT OF 2 CASES: We here present two cases of retroperitoneal dedifferentiated liposarcoma with a rare cystic presentation in two female patients aged 51 and 62 years. Imaging revealed large perinephric cystic masses measuring up to 13.0 cm and 16.1 cm, respectively, with calcifications of the cyst wall observed in the second case. Differential diagnoses included cystic echinococcosis, mesenchymal neoplasms, and benign cystic lesions (e.g. endometrial cyst). Both patients underwent upfront compartmental en-bloc surgical resection of the tumor mass and the kidney after multidisciplinary tumor board (MDT) discussion. Macroscopically, the tumors were adherent to but sharply demarcated from the kidney. Histological examination of the first case revealed a small component of well-differentiated liposarcoma (WDLPS) adjacent to a large non-lipogenic sarcoma with a prominent whirling pattern, compatible with dedifferentiation. The second case demonstrated a spindle cell neoplasm with prominent osteosarcomatous heterologous differentiation. MDM2 amplification was confirmed in both cases by molecular testing. No long-term follow-up data is available for either patient.

Conclusion: In conclusion, these cases highlight the importance of recognizing unusual and extensive cystic changes of dedifferentiated liposarcoma, which can complicate the diagnostic work-up.