Background. Diagnosis of dedifferentiated liposarcoma (DDL) can sometimes be challenging due to a wide variety of histological features. “Meningothelial-like” whorl is an uncommon histological feature of DDL, which is also observed in neural tumors and follicular dendritic cell sarcoma. This feature is frequently associated with metaplastic bone formation. We conducted this study to describe the clinicopathological features of DDL with meningothelial-like whorls that would aid in establishing accurate diagnosis. Material and Methods. Microscopic glass slides of 5 cases of DDL with meningothelial-like whorls, diagnosed between January 2010 and December 2019, were reviewed. Results. Paratesticular region was the most common site. Whorls occupied 10% to 75% of tumor area and ranged in size from <0.1 cm to >2 cm. In 1 case, these whorls coalesced to form large areas of dedifferentiation. The cells forming whorls were spindle to epithelioid shaped and lacked significant nuclear pleomorphism and increased mitoses. Metaplastic bone formation was observed in 4 cases and cartilage formation in 3 cases. p16 and α-smooth muscle actin (α-SMA) immunohistochemical stains were positive in 2 cases, when performed. MDM2 gene amplification was observed in all cases by fluorescence in situ hybridization technique. These tumors showed aggressive behavior, similar to that of DDL without meningothelial-like whorls. Two patients died, 1 developed recurrence, 1 presented as recurrent tumor, and 1 developed metastasis. Conclusion. Meningothelial-like whorls in DDL most likely represent an early stage of dedifferentiation. Presence of well-differentiated liposarcoma areas, metaplastic bone formation, positive expressions for p16 and α-SMA immunohistochemical stains, and MDM2 gene amplification are useful diagnostic clues. These tumors have the potential to behave aggressively.
A Case of Retroperitoneal Well-Differentiated Liposarcoma with Metaplastic Bone Formation