Cytopathology Case 13

Final Diagnosis & Discussions:

FINAL DIAGNOSIS: Thigh: Myxoid liposarcoma / Mesenteric Mass: Metastatic Myxoid Liposarcoma

 

DISCUSSION
Myxoid liposarcomas account for a significant minority of all liposarcomas (30% to 50%). Unlike other forms of liposarcoma, this form occurs in a younger age group with most presenting in the fifth decade. The masses preferentially involve the lower extremity (75%) with much less frequent mass formation in the retroperitoneum.

Microscopically, myxoid liposarcomas represent a continuum of lesions ranging from predominantly myxoid tumors with ample lipoblastic differentiation all the way to poorly differentiated round cell tumors wherein fatty differentiation is focal at best. The cytomorphology on FNA reflects the histologic features of the lesion. On FNA smears are composed of abundant myxoid (magenta on Diff Quik stain, light green on Papanicolaou stain), embedded “chicken-wire” or thin-walled capillaries, a proliferation of dispersed oval cells, and occasional multivacuolated lipoblasts. Our case demonstrated all of these features cytologically, with the exception of clearly identified lipoblasts on the FNA-obtained material. As lesions become more poorly differentiated their cyto-histologic characteristics become difficult to discern from other high grade sarcomas.

The primary differential diagnosis for a well-differentiated myxoid liposarcoma (as in this case) from a cytologic standpoint includes benign myxoid soft tissue lesions as well as other myxoid sarcomas. The primary entity to consider in the former category is a benign myxoma. While these growths can also exhibit the features of being deep-seated and often harbor an abundant myxoid matrix, they lack the characteristic vasculature and round cell proliferation. In fact, whenever there is an obvious blood vessel component to a myxoid soft tissue lesion on an FNA, one should always raise the possibility of a myxoid-type sarcoma and recommend an excisional biopsy. On the sarcoma end of the differential diagnostic spectrum, lesions that might simulate a myxoid liposarcoma are myxoid chondrosarcoma and low grade myxoid malignant fibrous histiocytoma (myxofibrosarcoma). The former is characterized by a more fibrillary-type magenta matrix with associated uniform, bland tumor cells in linear configurations with occasional lacunar forms. The latter tumor is characterized by significantly more nuclear atypia and a thicker vasculature than myxoid liposarcoma.

Nearly all myxoid liposarcomas are characterized by a reciprocal translocation between chromosomes 12 and 16: t(12;16)(q13;p11) termed the CHOP gene rearrangement. The clinical course of myxoid liposarcomas is dependent on several factors including age, tumor percentage of round cell population, and presence or absence of tumor necrosis. Those aged under 45, with no tumor necrosis, and <25% round cell change have the best 10 year survival rate. Finally, it should be noted that while myxoid lisposarcomas frequently metastasize to the usual sarcoma sites such as lung and bone, it has a curious predilection to metastasize to other soft tissue sites (as in this case).

References

  1. Richard M. DeMay. The Art & Science of Cytopathology. ASCP Press. 1996.

  2. Sharon W. Weiss and John Goldblum. Enzinger & Weiss’s Soft Tissue Tumors. Mosby Elsevier. 2008.

  3. Edmund S. Cibas and Barbara S. Ducatman. Cytology Diagnostic Principles and Clinical Correlates. Saunders Elsevier. 2009.

  4. Tomita H, Yamaguchi K, Matsuo M, Ohno T, Nishimoto Y, Hirose Y. Am Surg. 2006 Jan;72(1):68-70.