Primary intrathoracic liposarcoma: a clinical analysis of 31 cases

Primary intrathoracic liposarcomas: A clinicopathologic and molecular study of 43 cases in one of the largest medical centers of China

Introduction

Primary intrathoracic liposarcoma is extremely rare, and most published series lack genetic analyses. The aim of our study is to better understand the clinicopathologic and genetic features of these rare lesions.

Materials and methods

Forty-three primary intrathoracic liposarcomas were identified and most cases were analyzed by systematic genetic studies, including fluorescence in situ hybridization (FISH), whole-exome sequencing (WES), and Sanger sequencing.

Results

This series included 27 males and 16 females (ratios, 1.68:1) aged 24-73 years (median, 53 years). Tumors mainly occurred in the mediastinum (n=23, 53.5%), followed by pleural cavity (n=16, 37.2%) and lung (n=4, 9.3%). The study included 21 well-differentiated liposarcomas (WDLs), 19 dedifferentiated liposarcomas (DDLs), 2 myxoid pleomorphic liposarcomas (MPLs) and 1 pleomorphic liposarcoma (PL), without identification of myxoid liposarcoma. FISH analysis identified MDM2 amplification in 17 of 18 WDLs (94.4%) and all DDLs (16/16, 100.0%). The MDM2-nonamplified WDL was CDK4-nonamplified but FRS2-amplified. WES and Sanger sequencing found somatic TP53 mutation in the 2 MPLs. Follow-up information was available for 33 of 38 cases (86.8%). Thirteen patients (39.4%) showed no evidence of disease, 10 patients (30.3%) were alive with disease, and 8 patients (24.2%) died of disease. Fourteen cases developed recurrence and 1 with metastasis.

Conclusions

WDL/DDL was the overwhelming subtype in this location, followed by MPL and PL. Analysis of the FRS2 gene, in combination with MDM2 and other genes of 12q13-15, may more precisely characterize WDL/DDLs. MPL is the most fatal subtype of this site. Further studies are needed to explore the role of TP53 in the pathogenesis of MPL.

Liposarcomas of the mediastinum

Liposarcoma is a malignant tumor of adipocytic differentiation that rarely arises within the mediastinum. Most of the existing data available comes from scattered case reports and a few small series. The World Health Organization (WHO) recognizes four basic types of liposarcoma: well-differentiated/atypical lipomatous tumor (ALT), dedifferentiated, myxoid and pleomorphic liposarcoma (PLS). All of these liposarcoma subtypes have been recorded to occur within the mediastinum. On morphologic grounds liposarcoma can present a challenge for diagnosis as it can be difficult to distinguish from benign adipocytic neoplasms, or in the case of dedifferentiated liposarcoma (DDLS), from virtually any other type of sarcoma. Molecularly the most common subtypes of liposarcoma are characterized by specific, recurrent genetic alterations involving amplification events of MDM2 and CDK4 in well-differentiated liposarcoma (WDL) and a recurrent t(12;16)(q13;p11) in myxoid liposarcoma (MLS). MDM2 and CDK4 amplification can be assessed by immunohistochemistry, fluorescence in situ hybridization, or molecular techniques that evaluate copy number alterations and amplifications such as array based assays and next generation sequencing (NGS). In addition to WDL and MLS, a few additional rare subtypes of liposarcoma may occur in the mediastinum including PLS, myxoid WDL, thymoliposarcoma, and sclerosing high-grade liposarcoma. The present review will focus on the clinicopathologic features of the various histologic types of liposarcoma described in the mediastinum and their differential diagnosis. Data is derived from review of the largest series published in the more recent literature on these tumors.