[112] Dedifferentiated Liposarcoma with Inflammatory Myofibroblastic Differentiation

A Shukla, DG Thomas, AJ Kubat, DR Lucas. University of Michigan, Ann Arbor, MI; Spectrum Health, Grand Rapids, MI

Background: Dedifferentiated liposarcoma (DL) is defined by juxtaposition of well differentiated liposarcoma (WDL) and non-lipogenic sarcoma (NLS). In most tumors the NLS resembles pleomorphic undifferentiated sarcoma or myxofibrosarcoma. However, various patterns and heterologous lines of differentiation have been described. We have observed cases of DL with prominent myofibroblastic features associated with chronic inflammation that closely resemble inflammatory myofibroblastic tumor (IMT). Such tumors can potentially be misdiagnosed as IMT. To our knowledge this pattern has not been previously reported, nor has its morphologic, immunohistochemical and clinical spectrum.
Design: Among 35 DL diagnosed at our institution between 1990-2009, 6 had prominent IMT-like features. For each tumor we tabulated the extent of IMT-like histology (diffuse or focal), the subtype of WDL, and presence or absence of atypical cytological features within the IMT-like areas. Whole block sections were immunostained for IMT-associated markers (SMA, desmin, ALK-1) and liposarcoma-associated markers (MDM2, S-100).
Results: Mean age was 62 years (range 41-77) with a 5:1 male:female ratio. 2 (33%) were located in the inguinal/scrotal region, 2 (33%) in the retroperitoneum, 1 (17%) involved both inguinal/scrotal and retroperitoneum, and 1 (17%) was intraabdominal. Average tumor size was 19 cm (range 11-28). 4 (67%) were high-grade and 2 (33%) were low-grade. In 4 tumors (67%) the NLS component dominated, while in 2 it was a minor component. 2 tumors had diffuse IMT-like areas within the NLS component, while in 4 it was focal. 2 tumors had numerous ganglion-like fibroblasts, 2 had fibromatosis-like areas, 1 had osseous metaplasia, and 1 had a prominent nodular fasciitis-like appearance. 4 had atypical cells within the IMT-like areas. In 5 tumors (83%), the WDL was lipoma-like, while in 1 (17%) it was inflammatory WDL. SMA was positive in 4 tumors (67%), desmin in 4 (67%) and MDM2 in 2 (33%). No tumor showed ALK-1 or S-100 expression. Mean follow-up was 26 months (range 2-66). 3 patients had documented metastases, 3 had local recurrences, 2 died of disease, 2 were alive with disease, and 2 were alive without evidence of disease.
Conclusions: DL may have prominent myofibroblastic differentiation including areas indistinguishable from IMT, which may lead to misdiagnosis. These tumors have a predilection for the inguinal/scrotal region and retroperitoneum, are more common in men, and like conventional DL may show aggressive behavior.
Category: Bone & Soft Tissue

Monday, March 22, 2010 8:45 AM

Platform Session: Section F, Monday Morning


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