Liposarcomas with Mixed Well-Differentiated and Pleomorphic Features – A Clinicopathologic Study of 8 Cases

JM Boland, SW Weiss, AM Oliveira, ML Erickson-Johnson, AL Folpe. Mayo Clinic, Rochester, MN; Emory University, Atlanta, GA.

Background: Pleomorphic liposarcoma (PL) is defined as an undifferentiated pleomorphic sarcoma containing a variable number of pleomorphic lipoblasts. It is considered a distinct high grade sarcoma unrelated to other forms of liposarcoma since it almost always arises de novo without an associated low grade precursor lesions (e.g. well differentiatied liposarcoma (WDL)) and rarely co-exists with other liposarcoma patterns. We have, however, observed a small number of cases of PL which arose in association with WDL and have studied these cases to define their clinico-pathologic features and their nosologic relationship to other forms of liposarcoma.

Design: Cases showing the presence of both PL and WDL were retrieved from our consultation archives. The tumors were characterized at the molecular cytogenetic level for the presence of MDM2/CPM amplification when archival tumor blocks were available. One hundred cells were scored in each instance by two independent investigators. Follow-up information was obtained from the referring clinicians.

Results: Eight tumors were identified, occurring in 4 men and 4 women (mean age 55 years, range 35-78 years). Sites of origin included the retroperitoneum (3), scrotum (2), buttock (2), and abdominal cavity (1). Tumors consisted predominantly of typical WDL, with an “abrupt” transition to pleomorphic spindle cell sarcoma containing pleomorphic lipoblasts. MDM2/CPM amplification was present in 4 of 6 (66%) cases, all of which consisted chiefly of PL in the studied blocks. Clinical follow-up (6 of 8 (75%) patients; range 7-29 months; median 19 months) showed 5 patients alive without disease and 1 dead of disease.

Conclusions: PL with WDL is a rare pattern in liposarcoma. In the past such tumors were considered liposarcomas of mixed type to imply two distinct forms of liposarcoma occurring in the same lesion. The presence of MDM2/CPM amplification in the PL component of mixed WDL/PL suggest that a subset of PL may arise through tumor progression of WDL or may represent a “transitional” or partially differentiated step toward a classic DL. On-going review of a large cohort of tumors previously diagnosed as “DL” and additional molecular genetic study of both WDL and PL zones should clarify the relationship of these unusual tumors to classical DL, a tumor which by definition does not show lipoblastic differentiation.

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