[21] Liposarcoma of the Mediastinum and Thorax- 22 Cases in an Uncommon Location with Diverse and Unusual Histology

Jennifer M Boland, Thomas V Colby, Andrew L Folpe. Mayo Clinic, Rochester, MN; Mayo Clinic, Scottsdale, AZ

Background: Liposarcoma (LPS) rarely occurs in the mediastinum and thorax. Recent delineation of the genetic underpinnings of LPS has led to classification into three principal subtypes: well differentiated LPS/dedifferentiated LPS (WDL/DL), myxoid LPS (ML) and pleomorphic LPS (PL). Most previous reports of mediastinal LPS predate this genetically based classification. Herein we report the clinicopathologic and molecular genetic features of a series of thoracic LPS identified over a 60 year period.
Design: The consultation archives of the authors and surgical pathology database of our institution were searched for cases coded as lipoma and LPS of the mediastinum and thorax. The slides were reviewed, yielding 22 confirmed cases of LPS. Cases were reclassified using the most recent WHO classification. Follow up information was obtained from medical records and referring clinicians. Florescence in situ hybridization (FISH) for CPM amplification and/or DDIT3 (CHOP) rearrangement was performed on selected cases.
Results: The 22 cases occurred in 12 men and 10 women (mean 52 years, range 15-73). 21 cases arose primarily in the mediastinum (6 anterior, 6 posterior, 2 middle, 2 superior, 5 multiple compartments), and 1 arose in the inferior pleural space. The tumors were typically large (mean 15.7 cm, range 8-27 cm). All subtypes were encountered with 8 WDL, 5 DL (2 confirmed CPM+), 4 ML, 4 PL (one confirmed CPM-) and 1 unclassifiable liposarcoma (CPM- and DDIT3-). Unusual histologic features were noted in many cases, including extensively myxoid WDL mimicking ML (2 cases), WDL with low-grade smooth muscle differentiation (lipoleiomyosarcoma, 1 case), DL with osteosarcomatous and “meningothelial”-like dedifferentiation, extensively differentiated ML mimicking WDL (CPM-), and PL with epithelioid and myxoid change. Clinical follow up was available on all patients with a post-resection interval >12 months (mean follow up 60 months, range 12-252). Patient outcome varied significantly with histologic subtype, with death from disease occurring in 1 of 6 WDL, 1 of 4 DL, 3 of 4 ML and 4 of 4 PL.
Conclusions: Although all LPS subtypes may occur in the mediastinum, this location seems to show an unusual preponderance of uncommon subtypes (e.g., PL) as well as unusual morphological variants of common subtypes (e.g., myxoid WDL). Correct classification of mediastinal LPS has important clinical implications, with most patients with WDL/DL having a protracted clinical course, in contrast to the more rapid disease progression seen in patients with ML and PL.
Category: Bone & Soft Tissue

Monday, March 19, 2012 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 13, Monday Morning

 

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