Overlapping Features Between Dedifferentiated Liposarcoma and Undifferentiated High-Grade Pleomorphic Sarcoma

Epithelioid dedifferentiated liposarcoma: A clinicopathological and molecular study of 6 cases

In this study, we present six cases of epithelioid dedifferentiated liposarcoma to further characterize its clinical and pathological features. The patients are all adult men with age at presentation ranging from 46 to 64 years (median 58.5 years). The patients presented with nonspecific symptoms of retroperitoneal mass, intermittent dull pain or discomfort. None of the patients had any prior history of a primary tumor. Radiological examinations revealed the presence of ill-demarcated heterogenous mass located in the deep soft tissue, including retroperitoneum (4 cases), pelvis and trunk (1 case each). Grossly, they appeared as solid tumors with focal areas of necrosis being presented in 2 cases. Histologically, all tumors were characterized by sheets of epithelioid cells that displayed marked cellular atypia and brisk mitotic activity. Variable portion of atypical lipomatous tumor/well-differentiated liposarcoma was present in 3 cases. By immunohistochemistry, the high-grade epithelioid component in all 6 cases showed strong and diffuse nuclear staining of MDM2, CDK4 and P16, with partial expression of AE1/AE3 in 3 cases. Fluorescence in situ hybridization analysis revealed high-level amplification of MDM2 in all 6 cases, with co-amplification of CDK4 in 3 cases. Follow up information showed that two patients died of the disease within one year despite multidisciplinary treatment. Due to the striking epithelioid appearance, this rare variant of dedifferentiated liposarcoma may be confused with undifferentiated epithelioid sarcoma, poorly differentiated carcinoma, mesothelioma or other malignancies with epithelioid phenotype. The study presented herein further highlights the aggressive clinical behavior of this unique tumor type. For patients with advanced disease, CDK4 inhibitor may provide an optional targeted treatment.

Liposarcoma of the pleural cavity

Liposarcoma rarely occurs in the pleura or thoracic cavity, and few reports appear in the literature. We hypothesized that combining clinicopathologic, immunohistochemical, and fluorescence in situ hybridization methods would allow definite diagnoses. Using formalin-fixed, paraffin-embedded blocks, we examined 6 atypical lipomatous tumor/well-differentiated types (ALT/WDLPS), 5 dedifferentiated types (DDLPS), 2 pleomorphic types, and 1 myxoid type (MLSP). We used the Kaplan-Meier method and the Wilcoxon test for survival analysis for prognostic factor evaluation. Histologically, ALT/WDLPS was composed of a relatively mature adipocytic proliferation, accompanied by some lipoblasts. DDLPS exhibited round-to-oval tumor cells with a high nucleus-to-cytoplasm ratio that had proliferated in nests, accompanied in case 10 by some giant cells but no fatty cells. The pleomorphic type contained a varying proportion of pleomorphic lipoblasts. MLSP displayed uniform round to oval-shaped cells and small signet-ring lipoblasts in a myxoid stroma. Immunohistochemically, 11 (79%), 11 (79%), and 10 (71%) of 14 cases were positive for S-100, p16, and CDK4, respectively. Six (43%) of the 14 cases were positive for MDM2, and adipophilin. One case of ALT/WDLPS and 3 cases of DDLPS exhibited MDM2 amplification by fluorescence in situ hybridization (Vysis LSI MDM2 SpectrumGreen Probe plus Vysis CEP 12 SpectrumOrange probe). ALN/WDLPS was the most favorable type for survival, while adipophilin tended to be a negative prognostic factor for pleural liposarcoma. For a firm diagnosis of liposarcoma in the pleura, immunohistochemistry for CDK4, MDM2, and adipophilin together with MDM2 gene amplification by fluorescence in situ hybridization may be an important diagnostic tool.

Primary duodenal dedifferentiated liposarcoma: A case report and literature review

BACKGROUND

Dedifferentiated liposarcoma (DDLPS) is an extremely rare neoplasm that exhibits various morphologies. The tumor is characterized by immunoreactivity to MDM2 and CDK4 and can be confirmed by detecting MDM2 amplification via fluorescence in situ hybridization (FISH). Herein, we report an unusual case of DDLPS arising from the duodenum.

CASE SUMMARY

A 64-year-old man presented with repeated abdominal pain and weight loss. Radiologic studies revealed a mass of the duodenum involving the pancreas. The patient was treated with pylorus-preserving pancreaticoduodenectomy. Histologically, the tumor showed a high-grade sarcoma. Immunohistochemistry demonstrated that the tumor cells were positive for MDM2 and CDK4 expression. MDM2 amplification was detected via FISH, leading to the final diagnosis of DDLPS. Following surgery, the patient was treated in the intensive care unit due to peritonitis, and died 60 d after surgery.

CONCLUSION

To the best of the authors’ knowledge, this is the first case of primary duodenal DDLPS in Korea and the third case in the English-language literature. Care must be taken not to misdiagnose DDLPS as another high-grade tumor. Liposarcoma should be in the differential diagnosis list.

Undifferentiated and dedifferentiated soft tissue neoplasms: Immunohistochemical surrogates for differential diagnosis

Undifferentiated soft tissue sarcomas (USTS) are described in the current World Health Organization Classification of Soft Tissue and Bone Tumours as those showing no identifiable line of differentiation when analyzed by presently available technologies. This is a markedly heterogeneous group, and the diagnosis of USTS remains one of exclusion. USTS can be divided into four morphologic subgroups: pleomorphic, spindle cell, round cell and epithelioid undifferentiated sarcomas, with this combined group accounting for up to 20% of all soft tissue sarcomas. As molecular advances enable the stratification of emerging genetic subsets within USTS, particularly within undifferentiated round cell sarcomas, other groups, particularly the category of undifferentiated pleomorphic sarcomas (UPS), still remain difficult to substratify and represent heterogeneous collections of neoplasms often representing the common morphologic endpoints of a variety of malignant tumors of various (mesenchymal and non-mesenchymal) lineages. However, recent molecular developments have also enabled the identification and correct classification of many tumors from various lines of differentiation that would previously have been bracketed under 'UPS'. This includes pleomorphic neoplasms and dedifferentiated neoplasms (the latter typically manifesting with an undifferentiated pleomorphic morphology) of mesenchymal (e.g. solitary fibrous tumor and gastrointestinal stromal tumor) and non-mesenchymal (e.g. melanoma and carcinoma) origin. The precise categorization of 'pleomorphic' or 'undifferentiated' neoplasms is critical for prognostication, as, for example, dedifferentiated liposarcoma typically behaves less aggressively than other pleomorphic sarcomas, and for management, including the potential for targeted therapies based on underlying recurrent molecular features. In this review we focus on undifferentiated and dedifferentiated pleomorphic and spindle cell neoplasms, summarizing their key genetic, morphologic and immunophenotypic features in the routine diagnostic setting, and the use of immunohistochemistry in their principal differential diagnosis, and highlight new developments and entities in the group of undifferentiated and dedifferentiated soft tissue sarcomas.

Role of Radiation Therapy for Newly Diagnosed Retroperitoneal Sarcoma

OPINION STATEMENT

Soft tissue sarcomas (STS) are rare, aggressive, and heterogenous tumors, comprising approximately 1% of adult cancers with over 50 different subtypes. The mainstay of treatment for retroperitoneal sarcomas (RPS) includes surgical resection. The addition of radiation therapy (RT), either preoperatively or postoperatively, has been used to potentially decrease the risk of local recurrence. The recently published results from STRASS (EORTC-STBSG 62092-22092), which randomized patients to receive or not receive preoperative radiation, indicate no abdominal recurrence-free survival benefit (primary endpoint) nor overall survival benefit to date from the addition of preoperative RT prior to surgical resection in patients with RPS. Keeping in mind caveats of subgroup analyses, the data show a significant reduction in local recurrence with radiation therapy in resected patients and non-significant trends toward improved abdominal recurrence-free survival in all patients and improved local control and abdominal recurrence-free survival in patients with liposarcoma and low-grade sarcoma. Given the high rate of local failure with surgery alone, it is possible that higher RT dose and/or selective RT dose painting may improve outcomes. Prior to treatment, the authors encourage multidisciplinary review and discussion of management options at a sarcoma center for patients with RPS. Selective use of RT may be considered for patients at high risk of local recurrence.

Retroperitoneal Sarcomas: An Update on the Diagnostic Pathology Approach

Retroperitoneal sarcomas are a heterogenous group of rare tumors arising in the retroperitoneum. Retroperitoneal sarcomas comprise approximately 10% of all soft tissue sarcomas. Though any soft tissue sarcoma histologic types may arise in the retroperitoneal space, liposarcoma (especially well-differentiated and dedifferentiated types) and leiomyosarcoma do so most commonly. Retroperitoneal sarcomas are diagnostically challenging, owing to their diversity and morphological overlap with other tumors arising in the retroperitoneum. An accurate diagnosis is necessary for correct management and prognostication. Herein, we provide an update on the diagnostic approach to retroperitoneal sarcomas and review their key histologic findings and differential diagnoses.

A Case of Primary Duodenal Liposarcoma

Soft tissue sarcomas are common neoplasms accounting for 1% of all adult malignancies; however, soft tissue sarcomas infrequently arise from the abdominal viscera. Many case reports discuss gastric and esophageal neoplasms. In the group of gastrointestinal liposarcomas, primary duodenal liposarcomas are among the rarest, with only three previous cases reported in the literature. Herein, we discuss a case of primary duodenal liposarcoma. A 59-year-old woman presented with symptoms consistent with anemia raising suspicion for an upper gastrointestinal bleed. Upper endoscopy revealed an ulcerated mass in the first portion of the duodenum. The patient underwent a segmental duodenal resection and distal gastrectomy with Roux-en-Y reconstruction. A diagnosis of dedifferentiated liposarcoma was rendered on the resected specimen. At 16 months' follow-up, the patient remains without evidence of disease recurrence. We have presented a case of primary duodenal liposarcoma, which is among the rarest locations for gastrointestinal sarcomas with only three previous reports in the literature. Liposarcomas should be included in the differential for submucosal masses of the duodenum.

Retroperitoneal Tumor: A Silent Trespasser - Role of Image-Guided Fine-Needle Aspiration Cytology with Histopathological Correlation in Early Diagnosis

OBJECTIVE

Retroperitoneal lesions present a great diagnostic challenge. Here we analyze the spectrum of retroperitoneal lesions and the utility of cytohistopathological correlation in early diagnosis.

STUDY DESIGN

This 7-year study was undertaken in 338 patients with a retroperitoneal mass (kidney/adrenal/ pancreas/retroperitoneal lymph node, or soft tissue origin). In a prospective analysis, 81 patients underwent image-guided fine-needle aspiration cytology (FNAC) and 70 of the 81 underwent Tru-cut biopsy/histopathological evaluation. Clinical, radiological, and pathological details of 257 patients were retrieved from institutional records for retrospective analysis. A total of 119 patients, i.e., 70 in the prospective analysis and 49 in the retrospective analysis, had cytohistopathological correlation.

RESULTS

Of the 338 cases, 88.4% were malignant (n = 274), 2.6% were benign (n = 8), 9% were nonneoplastic (n = 28), and 9% were inadequate (n = 28). Most were renal in origin (n = 106; 34.2%), followed by retroperitoneal soft tissue (n = 96; 31%). The most common nonneoplastic lesion was tubercular lymphadenitis (42.85%) and the most common benign lesion was paraganglioma (42.85%). The most common malignancy was renal cell carcinoma (21.16%), followed by Wilms' tumor (13.86%). In infancy and early childhood, Wilms' tumor, neuroblastoma, and germ cell tumor were the most common malignancies, while in middle age it was renal cell carcinoma, followed by pancreatic adenocarcinoma, and in the elderly age group it was metastatic carcinoma. Most malignancies were noted in the 5th to 6th decades. The overall sensitivity, specificity, and diagnostic accuracy of image-guided FNAC was 98.02, 72.22, and 94.12%, respectively.

CONCLUSION

Image-guided FNAC is highly sensitive and specific for early diagnosis of an otherwise silent retroperitoneal mass. It saves patient from meticulous surgical procedures for diagnostic reasons and allows more rational planning of management. Knowledge of the distribution of tumors by age group helps to narrow down differential diagnoses.

Well-differentiated liposarcoma and dedifferentiated liposarcoma: An updated review

Well-differentiated liposarcoma (WDL)/atypical lipomatous tumor and dedifferentiated liposarcoma (DDL) together comprise the largest subgroup of liposarcomas, and constitute a histologic and behavioral spectrum of one disease. WDL and DDL typically occur in middle-aged to older adults, particularly within the retroperitoneum or extremities. WDL closely resembles mature adipose tissue, but typically shows fibrous septation with variable nuclear atypia and enlargement. WDL does not metastasize, but can dedifferentiate to DDL, which is associated with more aggressive clinical behavior, with a greater propensity for local recurrence and the capacity for metastasis. Although distant metastasis is rarer in DDL compared with other pleomorphic sarcomas, behavior is related to location, with a significantly worse outcome in retroperitoneal tumors. DDL typically has the appearance of undifferentiated pleomorphic or spindle cell sarcoma, and is usually a non-lipogenic sarcoma that is adjacent to WDL, occurs as a recurrence of WDL or which can arise de novo. WDL and DDL share similar background genetic aberrations; both are associated with high-level amplifications in the chromosomal 12q13-15 region, which includes the CDK4 and MDM2 cell cycle oncogenes. In addition, DDL harbor further genetic changes, particularly 6q23 and 1p32 coamplifications. While surgical excision remains the treatment mainstay with limited medical options for patients with aggressive recurrent disease or metastases, novel targeted therapies towards the gene products of chromosome 12 are being evaluated. This review summarizes the pathology of WDL and DDL, discussing morphology, immunohistochemistry, genetics and the differential diagnosis.

Diagnostic accuracy of percutaneous biopsy in retroperitoneal sarcoma

Background

Percutaneous biopsy is recommended before surgery for suspected retroperitoneal sarcoma (RPS) to confirm the histological diagnosis and guide surgical strategy. The present study aimed to establish the diagnostic accuracy of percutaneous core biopsy with respect to histological diagnosis and tumour grade.

Methods

Data on patients with suspected RPS who underwent percutaneous biopsy followed by surgical resection between 2005 and 2016 at one of two tertiary European sarcoma units were reviewed. Histological tumour type and tumour grade on biopsy were correlated with postoperative histology to evaluate diagnostic accuracy.

Results

A total of 239 patients underwent percutaneous core biopsy followed by surgical resection in Milan (163, 68·2 per cent) or Birmingham (76, 31·8 per cent). Diagnostic accuracy varied with histological diagnosis (P < 0·001), but demonstrated overall concordance with final pathology following resection in 67·2 per cent of biopsies (κ = 0·606). The majority of discrepancies occurred in dedifferentiated liposarcoma (DDLPS), owing to under-recognition of dedifferentiation in this group. Concordance between pathology on biopsy and resection improved to 81·1 per cent when DDLPS and well differentiated liposarcoma were grouped together as liposarcoma. Grade on biopsy was concordant with grade on resection specimen in 60·4 per cent of tumours (κ = 0·640). Diagnosis of high-grade tumours on biopsy had a high specificity (98 per cent), and moderate positive predictive value (85 per cent) and negative predictive value (78 per cent).

Conclusion

A diagnosis of DDLPS or leiomyosarcoma on percutaneous biopsy is highly reliable. High-grade sarcomas can be identified with high specificity, which opens the door to a study on neoadjuvant therapy in these patients.

Dedifferentiated Liposarcoma: Updates on Morphology, Genetics, and Therapeutic Strategies

Well-differentiated liposarcoma (WDL) and dedifferentiated liposarcoma (DDL) form the largest subgroup of liposarcomas, and represent a morphologic and behavioral spectrum of 1 disease entity, which arises typically in middle to late adult life, most frequently within the retroperitoneum or extremities. DDL is defined as nonlipogenic sarcoma that is juxtaposed to WDL, occurs as a recurrence of WDL or which can arise de novo, and typically has the appearance of undifferentiated pleomorphic or spindle cell sarcoma. DDL have a propensity for local recurrence, whereas distant metastasis is rarer, and behavior is related to anatomic site, with retroperitoneal neoplasms showing a significantly worse prognosis. Surgical resection remains the mainstay of treatment, and medical options for patients with aggressive recurrent or metastatic disease are limited. DDL share similar genetic abnormalities to WDL, with high-level amplifications of chromosome 12q14-15, including the MDM2 and CDK4 cell cycle oncogenes, and DDL harbor additional genetic changes, particularly coamplifications of 6q23 and 1p32. Novel therapies targeted at the gene products of chromosome 12 are being tested in clinical trials. We review the pathology and genetics of DDL, discussing morphologic patterns, immunohistochemical and genetic findings, the differential diagnosis, and future therapeutic strategies.

Amplification of FRS2 and activation of FGFR/FRS2 signaling pathway in high-grade liposarcoma

Fibroblast growth factor (FGF) receptor (FGFR) substrate 2 (FRS2) is an adaptor protein that plays a critical role in FGFR signaling. FRS2 is located on chromosome 12q13-15 that is frequently amplified in liposarcomas. The significance of FRS2 and FGFR signaling in high-grade liposarcomas is unknown. Herein, we first comparatively examined the amplification and expression of FRS2 with CDK4 and MDM2 in dedifferentiated liposarcoma (DDLS) and undifferentiated high-grade pleomorphic sarcoma (UHGPS). Amplification and expression of the three genes were identified in 90% to 100% (9-11 of 11) of DDLS, whereas that of FRS2, CDK4, and MDM2 were observed in 55% (41 of 75), 48% (36 of 75), and 44% (33/75) of clinically diagnosed UHGPS, suggesting that these "UHGPS" may represent DDLS despite lacking histologic evidence of lipoblasts. Immunohistochemical analysis of phosphorylated FRS2 protein indicated that the FGFR/FRS2 signaling axis was generally activated in about 75% of FRS2-positive high-grade liposarcomas. Moreover, we found that FRS2 and FGFRs proteins are highly expressed and functional in three high-grade liposarcoma cell lines: FU-DDLS-1, LiSa-2, and SW872. Importantly, the FGFR selective inhibitor NVP-BGJ-398 significantly inhibited the growth of FU-DDLS-1 and LiSa-2 cells with a concomitant suppression of FGFR signal transduction. Attenuation of FRS2 protein in FU-DDLS-1 and LiSa-2 cell lines decreased the phosphorylated extracellular signal-regulated kinase 1/2 and AKT and repressed cell proliferation. These findings indicate that analysis of FRS2 in combination with CDK4 and MDM2 will more accurately characterize pathologic features of high-grade liposarcomas. Activated FGFR/FRS2 signaling may play a functional role in the development of high-grade liposarcomas, therefore, serve as a potential therapeutic target.

Recurrent dedifferentiated paratesticular liposarcoma with synchronous renal cell carcinoma and prostate cancer

Paratesticular liposarcoma is a very rare cause of scrotal mass. It is thought that they arise from spermatic cord lipomas most commonly. While well differentiated tumors tend to share many histological similarities with dedifferentiated tumors, the latter has a much more aggressive phenotype. We present an unusual case of a 69-year-old male with synchronous prostate adenocarcinoma and unilateral renal cell carcinoma who was found to have a dedifferentiated paratesticular liposarcoma. Treatment was with radical resection, preserving the testis, followed by radiotherapy. Unusually recurrence did not occur until 4 years following initial treatment. This case demonstrates the high propensity of dedifferentiated liposarcoma to recur locally and examines the most frequently employed management strategies.

Expression of subtype-specific group 1 leiomyosarcoma markers in a wide variety of sarcomas by gene expression analysis and immunohistochemistry

Leiomyosarcomas (LMSs) constitute approximately one quarter of all sarcomas and are usually defined by morphologic criteria and/or immunoreactivity for actin or desmin. Among high-grade lesions, the distinction from undifferentiated pleomorphic sarcoma (UPS) can be problematic, and previous studies have shown that a significant number of LMS cases may be hiding under the diagnosis of UPS. We recently described 3 novel molecular LMS subtypes that are distributed similarly over LMSs of gyneocologic and non-gyneocologic origins. The group 1 subtype shows an improved disease-specific survival compared with the other 2 groups that is independent of histologic grade. Group 1 comprises approximately 25% of all LMSs, and is defined by a shared pattern of gene expression, a distinct pattern of genomic changes, and reactivity for at least 3 of 5 immunohistochemistry (IHC) markers (smooth muscle gamma actin, calsequestrin 2, human muscle cofilin2, myosin light chain kinase, and sarcolemmal membrane associated protein), as tested on 271 cases of LMS in tissue microarrays. These IHC markers have not been well characterized in non-LMS sarcomas. Here we provide a characterization of these 5 markers across normal tissues, an additional 59 cases of LMS, and a wide range of 565 non-LMS soft tissue tumors from 44 diagnostic categories, with a focus on UPS. When analyzed individually, the 5 markers were found to be expressed in many sarcomas other than LMSs. However, when analyzed by the same criteria used for the recognition of group 1 LMSs, in which a case is scored positive when at least 3 of 5 markers reacted, coordinate expression was seen in significant numbers of cases from only 3 diagnostic groups that included 22% of leiomyomas (n=22), 16% of gastrointestinal stromal tumors (n=43), and 18% of endometrial stromal sarcomas (n=11). In addition, 5% (n=57) of UPSs showed a staining pattern similar to that seen in group 1 LMSs. To further examine the possibility that group 1 LMS constitutes a small part of cases diagnosed as UPS, we examined the expression of the top 500 genes from the group 1 LMS expression signature in 29 UPSs by complementary DNA microarray. Unsupervised hierarchical clustering of 29 UPS expression showed that 2 (7%) had coordinated high levels of expression of genes from the group 1 LMS signature, a rate similar to that seen by IHC analysis. These findings show that group 1 LMS IHC markers smooth muscle gamma actin, calsequestrin 2, human muscle cofilin2, myosin light chain kinase, and sarcolemmal membrane associated protein when coordinately expressed have specificity for a subset of LMS when compared with other sarcomas, and may be useful for the recognition of group 1 LMS cases within cases diagnosed as UPS.

Immunohistochemistry in diagnosis of soft tissue tumours

Immunohistochemistry in soft tissue tumours, and especially sarcomas, is used to identify differentiation in the neoplastic cells. In some cases, specific antigens are expressed; however, an initial panel of antibodies is often required in order to establish the broad lineage, with a subsequent, more focused, panel to allow classification. Immunohistochemical evaluation must be employed with the clinical picture, the morphology, and, when necessary, other ancillary techniques such as molecular genetics and cytogenetics. Whereas some diagnoses are evident on morphology, many soft tissue neoplasms are seen microscopically as spindle cell, epithelioid cell, small round cell or pleomorphic tumours that need to be further characterized. This article reviews selected applications of immunohistochemistry in the diagnosis of each of the principal morphological groups, concentrating on areas of most use in daily practice.

Pleomorphic malignant fibrous histiocytoma/undifferentiated high-grade pleomorphic sarcoma of the scrotum in a patient presenting as fournier gangrene: a case report

Pleomorphic malignant fibrous histiocytoma (MFH), also known as undifferentiated high-grade pleomorphic sarcoma according to the latest World Health Organization classification, is a diagnosis of exclusion and extremely rare in adult scrotal/paratesticular region. Clinical presentation of scrotal/paratesticular pleomorphic MFH is usually a painless and gradual scrotal swelling. We report a case of scrotal MFH in a 63-year-old man who presented as Fournier gangrene after 10-month painful scrotal swelling and multiple procedures. The specimen of emergent debridement was submitted for pathologic and bacteriologic examination. Microscopically, the lesion had marked architectural and cytologic pleomorphism. The neoplastic cells were positive for vimentin, but negative for all lineage-specific markers. Fluorescence in-situ hybridization showed an aneuploid karyotype and negative results for lipomatous tumor abnormalities. Bacterial cultures of the specimen showed extensive growth of virulent polymicrobes. The diagnosis of scrotal/paratesticular pleomorphic MFH with concurrent Fournier gangrene was made. Thoracic computed tomography scan showed bilateral multiple pulmonary nodules. The patient died 1 month later.

Fine needle aspiration biopsy diagnosis of dedifferentiated liposarcoma: Cytomorphology and MDM2 amplification by FISH

Lipomatous mesenchymal tumors constitute the most common type of soft tissue tumors. Well-differentiated liposarcoma (WDLS) can undergo dedifferentiation to a nonlipogenic sarcoma of variable histologic grade. In the recent literature, amplification of the murine double minute 2 (MDM2) oncogene, which has a role in cell cycle control, has been successful in distinguishing WDLS from benign lesions. We present a case of dedifferentiated liposarcoma diagnosed by fine-needle aspiration (FNA), using cytomorphology and ancillary studies (immunocytochemistry and fluorescent in-situ hybridization). An 85-year old female presented to our institution with a firm soft tissue mass of the right buttock. The FNA showed atypical spindle cells, osteoclast-like giant cells and extracellular dense matrix material. The cell block showed cellular groups of highly atypical spindle cells with osteoid and adipose tissue. Fluorescence in situ hybridization (FISH) studies performed on the cell block demonstrated amplification of the MDM2 gene. In addition, the findings were morphologically compatible with the previously resected retroperitoneal dedifferentiated liposarcoma with areas of osteosarcoma. This rare case illustrates the usefulness of FNA and ancillary studies in the diagnosis and subclassification of soft tissue tumors. To the best of our knowledge, this is the first report of MDM2 FISH positivity in a liposarcoma diagnosed by FNA.