Well-differentiated mesenteric liposarcoma with osseous metaplasia: a potential diagnostic dilemma for the pathologist.

BACKGROUND: Mesenteric liposarcoma is a rare intra-abdominal sarcoma with very few cases reported in the available English literature. Incomplete resection of the tumor leads to recurrence, and recurrent tumors carry a risk of dedifferentiation. Dedifferentiation in liposarcoma manifests as a nonlipogenic sarcoma, which is usually high-grade and may show osteosarcomatous differentiation rarely. To the best of our knowledge, osteoid metaplasia in a well-differentiated liposarcoma without evidence of dedifferentiation has not been documented in the available literature. CASE: We describe the case of a middle-aged adult man with a well-differentiated liposarcoma of the mesentery. The patient presented with a recurrent tumor 5 years after the initial surgery. At recurrence, the histological features were those of a well-differentiated liposarcoma with focal osseous metaplasia without any evidence of dedifferentiation in the extensive sections examined.
CONCLUSION: Osseous metaplasia is a rare phenomenon in lipomas and dedifferentiated liposarcomas. Such an occurrence in a recurrent well-differentiated liposarcoma is a perplexing problem due to the potential confusion with dedifferentiation. This needs to be recognized to avoid overzealous chemotherapy and/or radiotherapy, which is required for dedifferentiated tumors.