Are Peripheral Purely Undifferentiated Pleomorphic Sarcomas With MDM2 Amplification Dedifferentiated Liposarcomas?

Superficial dedifferentiated liposarcoma: A clinicopathologic study

INTRODUCTION

Dedifferentiation occurs in approximately 10% of atypical lipomatous tumors/well-differentiated liposarcomas (ALT/WDLPS), primarily in retroperitoneal or deep-seated tumors, conferring metastatic potential. Superficial dedifferentiated liposarcoma (sDDLPS) is rare, and its progression and natural history are poorly documented.

METHODS

We performed a 15-year retrospective review of our pathology database to identify cases of DDLPS in the skin or subcutaneous tissue. Diagnosis of primary sDDLPS required evidence of non-lipogenic sarcoma in the skin or subcutis, with concurrent ALT/WDLPS and/or MDM2 amplification.

RESULTS

We identified 14 cases of DDLPS involving skin or subcutis: 7 primary sDDLPS and 7 secondary lesions (3 from recurrent deep DDLPS and 4 from metastasis). Primary sDDLPS cases (4 females, 3 males; median age: 74) mainly presented as undifferentiated spindle cell or pleomorphic sarcoma. Tumor grades were grade 2 (5 cases) and grade 3 (2 cases), with three cases also showing grade 1 areas. MDM2 amplification was confirmed in 6 sDDLPSs for which FISH was successfully performed. Follow-up available for 6 sDDLPS patients showed 2 local recurrences, treated with re-excision and radiation therapy, with all disease-free at last follow-up (5-126 months). Of the 7 secondary cases, 2 had ongoing disease after multiple recurrences, 1 was disease-free, and all 4 with cutaneous metastasis died of disease (follow-up range: 24-263 months).

CONCLUSION

These findings emphasize the importance of distinguishing between primary sDDLPS and secondary lesions due to their distinct prognoses. Metastasis or superficial extensions from deep DDLP correlate with a considerably worse prognosis than those originating in superficial tissues.

Analysis of clinical factors impacting recurrence in myxofibrosarcoma

Myxofibrosarcoma (MFS) is a malignant fibroblastic/myofibroblastic neoplasm with a prominent myxoid area. It has the clinical features of frequent local recurrence (LR) and occasional distant metastasis. Robust epidemiological data on MFS in China are lacking. The aim of this retrospective analysis was to determine the natural history of MFS, identify prognostic factors for recurrence and describe the real-life outcomes of MFS. We reviewed 52 patients with primary MFS from the First Affiliated Hospital of Nanjing Medical University diagnosed between 2016 and 2020. All tumors were subjected to retrospective univariate analysis for prognostic factors of the disease, including tumor size, grade, location and sex; patient age; planned operation; surgical margin; and laboratory results. The significant factors identified by univariate analysis were subsequently analyzed via multivariate analysis. Overall survival (OS), post-treatment LR and metastatic-free survival were assessed as outcomes. The median age was 61 years (range, 13-93). Fourteen (26.92%) patients exhibited low grade disease, and 38 (73.08%) exhibited high grade disease. Among the 29 males, and 23 females, 15 (28.85%) had tumors in the trunk, 37 (71.15%) had tumors in the extremities, 26 had undergone planned surgery, and 26 had unexpected unplanned operation. The margin was negative in 39 (75%) patients and positive in 13 patients (25%). The serum creatine kinase (CK) concentration was high level in 33 (63.46%) patients and low level in 19 (36.54%) patients. The serum lactate dehydrogenase (LDH) levels were low in 23 (44.23%) patients and high in 29 (55.77%) patients. LR was observed in 25 patients (48.08%), and 4 patients developed metastasis. A worse LR rate was found for patients with a low CK level (84.21%) than for those with a high CK level (27.27%) at 5 years (p < 0.05). The LR rate of patients who underwent planned surgery was lower than that of patients who underwent unplanned surgery (p < 0.05). There were significantly more patients with positive margins than patients with negative margins (92.30%, and 33.33%, respectively; p < 0.05). Moreover, superficial tumors were also associated with greater recurrence rate (2/20 [10%]) than deep tumors, (23/32 [71.86%]) [p < 0.05]. The probability of LR in patients with MFS was significantly greater in association with unplanned operations, positive margins, low serum CK levels or superficial tumor depth. These data could help identify high-risk patients; thus, more careful follow-up should be performed for higher-risk patients. Diagnosis and treatment at qualified regular medical centers can reduce the local recurrence rate of MFS.

Extremely Rare Type of Breast Cancer-Dedifferentiated Breast Liposarcoma-Diagnosis and Treatment

Primary liposarcoma of the breast is an uncommon soft tissue malignant tumor, comprising only 0.003% of all malignant breast tumors. The main differential diagnosis of this mass consists of malignant phyllodes tumor and metaplastic breast carcinoma. The objective of this paper is to report a case of dedifferentiated breast liposarcoma, therapeutic approach and outcome. We present a case of a 79-year-old woman complaining of a large mass in her left breast which had increased in size over the last 6 months. Physical examination revealed an enlarged left breast, and a total body CT scan showed a large tumor in contact with the musculature of the anterior thoracic wall, with no metastatic lesions. The histopathology report of a fine needle biopsy described a high-grade sarcoma. The Oncological Tumor Board recommended neoadjuvant radiotherapy sessions and reevaluation by MRI and CT scans. The patient underwent radical mastectomy with latissimus dorsi myo-cutaneous flap reconstruction. The final histopathology diagnosis was a grade 3 dedifferentiated liposarcoma (FNCLCC), with certain response to radiotherapy and positive MDM2, CDK4 markers. The postoperative period was uneventful; 12 months after surgery, the follow-up CT scan showed multiple pulmonary lesions with metastatic characteristics. Liposarcoma is a very rare type of breast cancer, and the most important treatment for breast sarcoma is surgery, the role of axillary lymph node removal, chemotherapy and radiotherapy still being controversial. Considering such cases are scarce and the development of surgical guidelines is difficult, reporting any new case is crucial.

Primary cardiac sarcomas: A clinicopathologic study in a single institution with 25 years of experience with an emphasis on MDM2 expression and adjuvant therapy for prognosis

BACKGROUND

Primary cardiac sarcomas are rare and their clinicopathologic features are heterogeneous. Among them, particularly intimal sarcoma is a diagnostic challenge due to nonspecific histologic features. Recently, MDM2 amplification reported to be a characteristic genetic event in the intimal sarcoma. In this study, we aimed to identify the types and incidence of primary cardiac sarcomas that occurred over 25 years in tertiary medical institutions, and to find clinicopatholgical significance through reclassification of diagnoses using additional immunohistochemistry (IHC).

METHODS

We reviewed the primary cardiac sarcoma cases between January 1993 and June 2018 at Asan Medical Center, South Korea, with their clinicopathologic findings, and reclassified the subtypes, especially using IHC for MDM2 and then, analyzed the significance of prognosis.

RESULTS

Forty-eight (6.8%) cases of a primary cardiac sarcoma were retrieved. The tumors most frequently involved the right atrium (n = 25, 52.1%), and the most frequent tumor subtype was angiosarcoma (n = 23, 47.9%). Seven cases (53.8%) were newly reclassified as an intimal sarcoma by IHC for MDM2. Twenty-nine (60.4%) patients died of disease (mean, 19.8 months). Four patients underwent a heart transplantation and had a median survival of 26.8 months. This transplantation group tended to show good clinical outcomes in the earlier stages, but this was not statistically significant (p = 0.318). MDM2 positive intimal sarcoma showed the better overall survival (p = 0.003) than undifferentiated pleomorphic sarcoma. Adjuvant treatment is beneficial for patient survival (p < 0.001), particularly in angiosarcoma (p < 0.001), but not in intimal sarcoma (p = 0.154).

CONCLUSION

Our study supports the use of adjuvant treatment in primary cardiac sarcoma, as it was associated with a significantly better overall survival rate. Further consideration of tumor histology may be important in determining the optimal use of adjuvant treatment for different types of sarcomas. Therefore, accurate diagnosis by MDM2 test is important condsidering patient's prognosis and treatment.

The Recent Advances in Molecular Diagnosis of Soft Tissue Tumors

Soft tissue tumors are rare mesenchymal tumors with divergent differentiation. The diagnosis of soft tissue tumors is challenging for pathologists owing to the diversity of tumor types and histological overlap among the tumor entities. Present-day understanding of the molecular pathogenesis of soft tissue tumors has rapidly increased with the development of molecular genetic techniques (e.g., next-generation sequencing). Additionally, immunohistochemical markers that serve as surrogate markers for recurrent translocations in soft tissue tumors have been developed. This review aims to provide an update on recently described molecular findings and relevant novel immunohistochemical markers in selected soft tissue tumors.

Head pleomorphic sarcoma showing murine double minute 2 amplification without a well-differentiated liposarcoma component in a pediatric patient

BACKGROUND

Murine double minute 2 (MDM2) is an oncogene that inhibits p53, leading to decreased apoptosis. Sarcomas showing MDM2 amplification are rare among pediatric patients.

CASE

A 14-year-old boy presented with pleomorphic sarcoma of the head showing MDM2 amplification without a well-differentiated liposarcoma component. Although chemotherapy was initially performed to reduce the tumor size before surgery, the tumor did not shrink. The patient underwent complete surgical resection. Microscopic examination revealed a positive surgical margin; thus, postoperative proton-beam radiotherapy was performed. 3 years after the therapy, no sign of recurrence was observed.

CONCLUSION

Macroscopic surgical resection combined with adjuvant postoperative radiotherapy was effective against MDM2-amplified pleomorphic sarcoma refractory to neoadjuvant chemotherapy in a pediatric patient.

The Characteristics of magnetic resonance imaging and immunohistochemical findings in de-differentiated liposarcoma

PURPOSE

Radiological imaging in Dedifferentiated liposarcoma (DDLPS) often shows the coexistence of fatty and non-fatty solid components; however, it has been shown that when fatty components were not identified on magnetic resonance imaging (MRI), the diagnosis of DDLPS would not have been diagnosed if immunohistochemical (IHC) staining had not been performed. The aim of this study was to investigate the pattern of MRI and relationship between MRI and IHC findings in DDLPS.

METHODS

We retrospectively reviewed the cases of 25 patients with DDLPS. To identify the MRI spectrum of DDLPS, tumors were classified into the following four categories based on MRI findings: I = a well-defined fatty mass and juxtaposed well-defined non-fatty mass, II = a non-fatty component within a predominantly fatty mass, III = a focal fatty component within a large non-fatty mass, and IV = a non-fatty mass with atypical MRI findings. IHC staining for CDK4, MDM2, and p16 were evaluated.

RESULTS

Category IV tumor was the most common tumor in this population. Of the 22 patients who underwent IHC staining, MDM2, CDK4, and p16 were positive in 21, 20, and 19 patients, respectively. MDM2 was positive in all 11 patients with category IV tumors; CDK4 and p 16 were positive in 10 and eight patients, respectively. There was no difference of survival between the patients with category I, II and III and category IV.

CONCLUSIONS

DDLPS without fatty components on MRI scans was mostly found. We recommend IHC staining to screen for DDLPS even if the tumors in STS cases have a non-fatty component.

Retroperitoneal liposarcoma with pancreatic metastasis and gastric cancer: a case report

On computed tomography scanning, a 63-year-old man with vomiting and anorexia was discovered to have a mass in the pancreatic body and a retroperitoneal mass extending to the right lobe of the liver. An esophagogastroduodenoscopy revealed an advanced gastric carcinoma in the middle gastric body, and a biopsy specimen revealed a poorly differentiated adenocarcinoma. The pancreatic and retroperitoneal masses were considered metastatic lesions of gastric cancer, and a biopsy was taken from the pancreatic lesion using endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA). The histology of the EUS-FNA pancreatic specimen revealed atypical spindle-shaped cells and increased stromal collagen fibrosis, and liposarcoma was considered. Conversely, a percutaneous ultrasound-guided biopsy was taken for the retroperitoneal lesion, and the histology revealed that it was a dedifferentiated liposarcoma. On the basis of histopathological and imaging findings, the retroperitoneal liposarcoma was identified as the primary lesion, the pancreatic lesion as a metastasis of the primary liposarcoma, and the gastric carcinoma as an independent tumor. As far as we know, there have only been three reports of metastatic pancreatic liposarcoma diagnosed via EUS-FNA. In this case, the patient also had gastric cancer, and EUS-FNA was helpful in differentiating metastatic pancreatic tumors from gastric cancer.

MRI findings to differentiate musculoskeletal dedifferentiated liposarcoma from atypical lipomatous tumor

OBJECTIVE

This study aimed to assess the efficacy of using MRI findings for differentiating musculoskeletal dedifferentiated liposarcoma (DDLP) from atypical lipomatous tumor (ALT).

MATERIALS AND METHODS

This study included 22 patients with histopathologically proven DDLP and 35 with ALT in the musculoskeletal areas. All DDLPs were immunohistochemically positive for MDM2. MRI findings for both pathologies were retrospectively reviewed and compared.

RESULTS

The maximum lesion diameter was significantly lower in DDLPs than in ALTs (p < 0.01). Ill-defined margin, peritumoral edema, and tail sign were more frequently observed in DDLPs than in ALTs (p < 0.01, respectively). The fatty component was less frequently observed in DDLPs than in ALTs (27 vs. 100%; p < 0.01), whereas the non-fatty component was more frequently observed in DDLPs than in ALTs (100 vs. 11%; p < 0.01). The occupation rate by non-fatty components was significantly higher in DDLPs than in ALTs (p < 0.01). No significant differences were observed in imaging findings associated with fatty component; however, necrosis within the non-fatty component on the contrast-enhanced image was more frequently observed in DDLPs than in ALTs (72 vs. 0%, p < 0.05).

CONCLUSION

DDLPs always had a non-fatty component, whereas ALTs always had fatty component. Ill-defined margin, peritumoral edema, tail sign, and necrosis within non-fatty components were useful MRI features for differentiating musculoskeletal DDLP from ALT.

Histopathological Correlation of Chromosome 12 Polysomy by Fluorescence in Situ Hybridization in Adipocytic Neoplasms

Background: Identification of MDM2 amplification by fluorescence in situ hybridization is an important diagnostic tool for evaluation of adipocytic neoplasms. Rarely, neoplasms can show increased copies of MDM2 and CEP12 probes (polysomy) without amplification (MDM2/CEP12 ratio <2.0). While noted in the literature, this finding has not been the focus of any study to date. Methods: Consecutive cases were retrospectively screened for increased copies of MDM2 and CEP12 and were classified as: high polysomy (ratio<2.0, CEP12≥10.0), low polysomy (ratio<2.0, but >0.5, CEP12≥4.0 but <9.9), and CEP12 amplification (ratio≤0.5, CEP12 > 4.0). H&E slides were classified by a pathologist into diagnostic categories based on morphology without knowledge of MDM2 amplification result. Correlations between chromosome 12 polysomy and histological features in the same region of the tumor were investigated. Results: There were 19 (0.7%) high polysomy, 52 (2.0%) low polysomy and 3 (0.1%) CEP12 amplification cases identified in the 2541 cases screened. While low polysomy was seen across benign and malignant adipocytic tumors and other sarcomas, high level polysomy was primarily seen in liposarcomas, both atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDLPS) and dedifferentiated liposarcoma (DDLPS). No lipomas were high polysomy. Conclusion: Polysomy is an uncommon, but distinct, finding in adipocytic neoplasms found across the spectrum of benign to malignant with little insight into the pathophysiology or prognosis. While low polysomy is also observed in benign adipocytic neoplasms, high polysomy is almost always seen in malignant adipocytic neoplasms and is uncommon in benign adipocytic neoplasms.

Accuracy of core needle biopsy for histologic diagnosis of soft tissue sarcoma

The biopsy technique of choice in soft tissue sarcoma (STS) diagnosis is controversial. We examined the diagnostic accuracy of percutaneous core needle biopsy (CNB) and compared it to open incisional biopsy. A retrospective study included 91 incisional biopsies and 102 CNBs. A pair-match investigation was conducted on 19 patient pairs, comparing sensitivity, specificity, and diagnostic accuracy. Furthermore, we investigated the role of molecular pathology in sarcoma diagnostics. In 81/91 (89%) patients with incisional biopsy, the entity was confirmed by definitive pathology, whereas this was the case in 89/102 (87%) CNB patients (p = 0.52). Grading remained unchanged in 46/55 (84%) of incisional and 54/62 (87%) of CNBs (p = 0.61). The pair matched analysis showed that the correct entity was determined in 96% of incisional and 97.6% of core needle biopsies. The time between the initial consultation and the interdisciplinary tumor board's treatment recommendation was shorter in core needle biopsies (8.37 vs. 15.63 days; p < 0.002). Incisional biopsies led to two wound infections and one hematoma, whereas wound infection occurred in one patient after CNB. CNB leads to faster diagnosis while reaching the same histological accuracy and is less burdensome for patients. Still, surgeons need to remain aware of the possibility of biopsy failure.

Noncanonical roles of p53 in cancer stemness and their implications in sarcomas

Impairment of the prominent tumor suppressor p53, well known for its canonical role as the "guardian of the genome", is found in almost half of human cancers. More recently, p53 has been suggested to be a crucial regulator of stemness, orchestrating the differentiation of embryonal and adult stem cells, suppressing reprogramming into induced pluripotent stem cells, or inhibiting cancer stemness (i.e., cancer stem cells, CSCs), which underlies the development of therapy-resistant tumors. This review addresses these noncanonical roles of p53 and their implications in sarcoma initiation and progression. Indeed, dysregulation of p53 family proteins is a common event in sarcomas and is associated with poor survival. Additionally, emerging studies have demonstrated that loss of wild-type p53 activity hinders the terminal differentiation of mesenchymal stem cells and leads to the development of aggressive sarcomas. This review summarizes recent findings on the roles of aberrant p53 in sarcoma development and stemness and further describes therapeutic approaches to restore normal p53 activity as a promising anti-CSC strategy to treat refractory sarcomas.

Clinicopathological and Histopathological Review of Dedifferentiated Liposarcoma: A Comprehensive Study of 123 Primary Tumours

AIMS

Dedifferentiated liposarcoma (DDLS) exhibits varying histopathological features, but their significance for the biological behaviour of this disease has not been fully clarified. This study aimed at elucidating the prognostic factors of DDLS by clinicopathologically reviewing a large case series.

METHODS AND RESULTS

We clinicopathologically reviewed 123 cases of primary de novo DDLS without preoperative treatment, including 81 in the internal trunk (internal DDLS) and 42 in peripheral sites (peripheral DDLS). Univariate and multivariate analyses of their features were also performed for all cases, the internal DDLS group, and the peripheral DDLS group. The results showed that, in all three groups, distant metastasis was significantly associated with shorter overall survival (OS) (univariate analysis, P<0.0001, =0.0011, and 0.0101, respectively), whereas local recurrence showed no significant effect on prognosis. Histopathologically, high mitotic count and the presence of round tumour cells were significantly associated with shorter OS in multivariate analysis of the internal DDLS group (P=0.0022, HR=4.39, 95% CI 1.71-11.28; P=0.0014, HR=7.19, 95% CI 2.14-24.16, respectively). Meanwhile, in the peripheral DDLS group, necrosis and high-grade histological components were significantly associated with shorter OS (univariate analysis, P=0.0068 and 0.0174, respectively).

CONCLUSIONS

The presence of round tumour cells may be one of the histological factors associated with a worse prognosis in DDLS, as previous studies indicated. This work also suggested that distant metastasis may be predictive of prognosis in both internal and peripheral DDLS, instead of local recurrence.

MDM2 Amplified Sarcomas: A Literature Review

Murine Double Minute Clone 2, located at 12q15, is an oncogene that codes for an oncoprotein of which the association with p53 was discovered 30 years ago. The most important function of MDM2 is to control p53 activity; it is in fact the best documented negative regulator of p53. Mutations of the tumor suppressor gene p53 represent the most frequent genetic change in human cancers. By overexpressing MDM2, cancer cells have another means to block p53. The sarcomas in which MDM2 amplification is a hallmark are well-differentiated liposarcoma/atypical lipomatous tumor, dedifferentiated liposarcoma, intimal sarcoma, and low-grade osteosarcoma. The purpose of this review is to summarize the typical clinical, histopathological, immunohistochemical, and genetic features of these tumors.

OSIRIS: A Minimum Data Set for Data Sharing and Interoperability in Oncology

PURPOSE

Many institutions throughout the world have launched precision medicine initiatives in oncology, and a large amount of clinical and genomic data is being produced. Although there have been attempts at data sharing with the community, initiatives are still limited. In this context, a French task force composed of Integrated Cancer Research Sites (SIRICs), comprehensive cancer centers from the Unicancer network (one of Europe's largest cancer research organization), and university hospitals launched an initiative to improve and accelerate retrospective and prospective clinical and genomic data sharing in oncology.

MATERIALS AND METHODS

For 5 years, the OSIRIS group has worked on structuring data and identifying technical solutions for collecting and sharing them. The group used a multidisciplinary approach that included weekly scientific and technical meetings over several months to foster a national consensus on a minimal data set.

RESULTS

The resulting OSIRIS set and event-based data model, which is able to capture the disease course, was built with 67 clinical and 65 omics items. The group made it compatible with the HL7 Fast Healthcare Interoperability Resources (FHIR) format to maximize interoperability. The OSIRIS set was reviewed, approved by a National Plan Strategic Committee, and freely released to the community. A proof-of-concept study was carried out to put the OSIRIS set and Common Data Model into practice using a cohort of 300 patients.

CONCLUSION

Using a national and bottom-up approach, the OSIRIS group has defined a model including a minimal set of clinical and genomic data that can be used to accelerate data sharing produced in oncology. The model relies on clear and formally defined terminologies and, as such, may also benefit the larger international community.

Intimal sarcomas and undifferentiated cardiac sarcomas carry mutually exclusive MDM2, MDM4, and CDK6 amplifications and share a common DNA methylation signature

Undifferentiated mesenchymal tumors arising from the inner lining (intima) of large arteries are classified as intimal sarcomas (ISA) with MDM2 amplification as their molecular hallmark. Interestingly, undifferentiated pleomorphic sarcomas (UPS) of the heart have recently been suggested to represent the cardiac analog of ISA due to morphological overlap and high prevalence of MDM2 amplifications in both neoplasms. However, little is known about ISAs and cardiac UPS without MDM2 amplifications and molecular data supporting their common classification is sparse. Here, we report a series of 35 cases comprising 25 ISAs of the pulmonary artery, one ISA of the renal artery and 9 UPS of the left atrium. Tumors were analyzed utilizing the Illumina Infinium MethylationEPIC BeadChip array, enabling copy number profile generation and unsupervised DNA methylation analysis. DNA methylation patterns were investigated using t-distributed stochastic neighbor embedding (t-SNE) analysis. Histologically, all ISAs and UPS of the left atrium resembled extra-cardiac UPS. All cases exhibited highly complex karyotypes with overlapping patterns between ISA and UPS. 29/35 cases showed mutually exclusive amplifications in the cell-cycle associated oncogenes MDM2 (25/35), MDM4 (2/35), and CDK6 (2/35). We further observed recurrent co-amplifications in PDGFRA (21/35), CDK4 (15/35), TERT (11/35), HDAC9 (9/35), and CCND1 (4/35). Sporadic co-amplifications occurred in MYC, MYCN, and MET (each 1/35). The tumor suppressor CDKN2A/B was frequently deleted (10/35). Interestingly, DNA methylation profiling (t-SNE) revealed an overlap of ISA and cardiac UPS. This "ISA" methylation signature was distinct from potential histologic and molecular mimics. In conclusion, our data reveal MDM4 and CDK6 amplifications in ISAs and UPS of the left atrium, lacking MDM2 amplification. We further report novel co-amplifications of various oncogenes, which may have therapeutic implications. Finally, the genetic and epigenetic concordance of ISAs and UPS of the left atrium further supports a shared pathogenesis and common classification.

[Fluorescence in situ hybridization for the diagnosis of soft-tissue and bone tumors]

Mesenchymal tumors, especially high-grade sarcomas, frequently harbor chaotic genotypes. Few tumors arise in association with genetic tumor predisposition syndromes with germline mutations in tumor suppressor genes. An increasing number of soft-tissue and bone tumors are characterized by recurrent genomic alterations, which can be utilized for diagnostic purposes. These include translocations and amplifications and less frequently deletions. These alterations can be detected by fluorescence in situ hybridization among other techniques. The rising number of whole genome sequencing of soft-tissue and bone tumors leads to an improved understanding of tumor genetics. On this basis, fluorescence in situ hybridization has gained relevance as a diagnostic tool. This review covers relevant genetic alterations in lipomatous tumors, soft-tissue tumors with spindle-cell and epithelioid morphology, vascular tumors, small-blue-round-cell tumors, and bone tumors that are detectable by fluorescence in situ hybridization.

Establishment and characterization of NCC-DDLPS1-C1: a novel patient-derived cell line of dedifferentiated liposarcoma

Dedifferentiated liposarcoma (DDLPS) is one of the four subtypes of liposarcomas; it is characterized by the amplification of the 12q13-15 region, which includes MDM2 and CDK4 genes. DDLPS has an extremely high local recurrence rate and is refractory to chemotherapy and radiation, which leads to poor prognosis. Therefore, a novel therapeutic strategy should be urgently established for improving the prognosis of DDLPS. Although patient-derived cell lines are important tools for basic research, there are no DDLPS cell lines available from public cell banks. Here, we report the establishment of a novel DDLPS cell line. Using the surgically resected tumor tissue from a patient with DDLPS, we established a cell line and named it NCC-DDLPS1-C1. The NCC-DDLPS1-C1 cells contained 12q13-15, 1p32, and 1q23 amplicons and highly expressed MDM2 and CDK4 proteins. NCC-DDLPS-C1 cells exhibited constant growth, spheroid formation, aggressive invasion, and tumorigenesis in mice. By screening a drug library, we identified that the proteasome inhibitor, bortezomib, had inhibitory effects on the proliferation of NCC-DDLPS1-C1 cells. We concluded that the NCC-DDLPS1-C1 cell line may serve as a useful tool for basic and pre-clinical studies of DDLPS.

Diagnostic Utility and Limitations of Immunohistochemistry of p16, CDK4, and MDM2 and Automated Dual-color In Situ Hybridization of MDM2 for the Diagnosis of Challenging Cases of Dedifferentiated Liposarcoma

The diagnosis of dedifferentiated liposarcoma (DDLPS) is challenging when an atypical lipomatous tumor component is absent or obscure. To analyze the utility and limitations of ancillary techniques, we studied 11 cases of DDLPS in challenging conditions and 17 cases of nonlipogenic high-grade sarcomas with immunohistochemistry (IHC) for p16, CDK4, and MDM2 and automated dual-color in situ hybridization (DISH) for MDM2 amplification. All DDLPS specimens lacked clear lipogenic components and were immunoreactive for p16, CDK4, and MDM2. DISH analyses also revealed high-level amplification of MDM2 in all DDLPS. In contrast, among nonlipogenic sarcomas, p16, CDK4, and MDM2 were expressed in 8, 9, and 3 cases, respectively. MDM2 amplification was detected in 3 of 8 studied. The MDM2-amplified tumors were the same as the MDM2-immunoreactive tumors. After careful reevaluation of these 3 sarcomas, 2 were reclassified as DDLPS because small areas of lipogenic components were detected in the original specimens. The respective sensitivities and specificities of these markers were as follows: p16 IHC (100% and 60%), CDK4 IHC (100% and 53.3%), MDM2 IHC (100% and 93.3%), and MDM2 DISH (100% and 83.3%). The results of MDM2 IHC completely coincided with those of MDM2 DISH. The present study confirmed the substantial utility of MDM2 IHC and MDM2 DISH in the diagnosis of DDLPS, especially when lipogenic components were indistinct compared with IHC for p16 and CDK4. Furthermore, automated DISH was more practical than fluorescent in situ hybridization.

Comparative Study of Myxofibrosarcoma With Undifferentiated Pleomorphic Sarcoma: Histopathologic and Clinicopathologic Review

Myxofibrosarcoma (MFS) is a malignant fibroblastic/myofibroblastic neoplasm with the prominent myxoid area. It has the clinical features of frequent local recurrence and occasional distant metastasis. Morphologically, MFS is occasionally difficult to distinguish from undifferentiated pleomorphic sarcoma (UPS), especially in the case of high-grade MFS. Here, we reviewed clinical and histologic data of 162 MFS cases and 43 UPS cases. MFS was distinguished from UPS with the criterion of 10% myxoid area as a cutoff value. Overall, 52 MFS (34.4%) and 9 UPS (20.9%) cases showed local recurrence, 18 MFS (12.2%) and 19 UPS (44.2%) cases developed distant metastasis, and 13 MFS (9.5%) and 14 UPS (32.6%) cases resulted in tumor-related death. Statistically, MFS had a better prognosis than UPS. Moreover, MFS with less myxoid area had a tendency to present a poorer prognosis. FNCLCC grade was a statistically significant prognostic factor (distant metastasis: P=0.0021, tumor-related death: P=0.0021). Cellularity and nuclear atypia had only a statistical tendency for associations with a poorer prognosis. The overall survival rate of MFS after transformation into a UPS-like condition (<10% myxoid area) was close to that of UPS. It was suggested that MFS is a biologically distinct tumor from UPS, and MFS with less myxoid area had a tendency to present a poorer prognosis. We considered that evaluation of the amount of myxoid area, cellularity, and nuclear atypia may be important as prognostic predictors. MFS may become similar to histologic malignancy of UPS in terms of morphology and biology via local recurrence.

p53 dynamics in single cells are temperature-sensitive

Cells need to preserve genome integrity despite varying cellular and physical states. p53, the guardian of the genome, plays a crucial role in the cellular response to DNA damage by triggering cell cycle arrest, apoptosis or senescence. Mutations in p53 or alterations in its regulatory network are major driving forces in tumorigenesis. As multiple studies indicate beneficial effects for hyperthermic treatments during radiation- or chemotherapy of human cancers, we aimed to understand how p53 dynamics after genotoxic stress are modulated by changes in temperature across a physiological relevant range. To this end, we employed a combination of time-resolved live-cell microscopy and computational analysis techniques to characterise the p53 response in thousands of individual cells. Our results demonstrate that p53 dynamics upon ionizing radiation are temperature dependent. In the range of 33 °C to 39 °C, pulsatile p53 dynamics are modulated in their frequency. Above 40 °C, which corresponds to mild hyperthermia in a clinical setting, we observed a reversible phase transition towards sustained hyperaccumulation of p53 disrupting its canonical response to DNA double strand breaks. Moreover, we provide evidence that mild hyperthermia alone is sufficient to induce a p53 response in the absence of genotoxic stress. These insights highlight how the p53-mediated DNA damage response is affected by alterations in the physical state of a cell and how this can be exploited by appropriate timing of combination therapies to increase the efficiency of cancer treatments.

The genomics of undifferentiated sarcoma of soft tissue: Progress, challenges and opportunities

Undifferentiated sarcoma of soft tissue (USTS) are aggressive sarcomas that remain a diagnosis of exclusion and show extreme genomic complexity. Many advances in diagnostic criteria have resulted in several revisions in the definition of this rare cancer type. Recent sequencing efforts have illuminated the nature of the genome complexity and have revealed extensive copy number heterogeneity and multiple evolutionary patterns of development. This review places these recent advances into their historical and translational context and covers the changes in nomenclature, molecular classification, and the promise of personalised medicine.

Immunohistochemistry as a Genetic Surrogate in Dermatopathology: Pearls and Pitfalls

Immunohistochemistry (IHC) is routinely performed in most laboratories, and other than purchase of commercially available antibodies, requires no additional equipment or reagents. As such, IHC is an accessible and relatively inexpensive test and one that can be performed quite quickly. This is in sharp contrast to genomic or mutational testing methodologies that are routinely "send out" tests as they require specialized equipment and reagents as well as individuals with expertise in the performance of the tests and analysis of the results, resulting in a prolonged turn-round-time and enhanced associated costs. However, many open questions remain in a rapidly changing therapeutic and scientific landscape with most obvious one being what exactly is the utility of "good old fashioned" IHC in the age of targeted therapy? For molecular applications, is a negative immunohistochemical result enough as a stand-alone diagnostic or predictive product? Is a positive immunohistochemical result perhaps more suitable for a role in screening for molecular alterations rather than a definitive testing modality? This review is an attempt to answer those very questions. We elucidate the broad range of entities in which IHC is currently used as a molecular surrogate and underscore pearls and pitfalls associated with each. Special attention is given to entities for which targeted therapies are currently available and to entities in which molecular data is of clinical utility as a prognosticator.

[Tumors with predominantly adipocytic morphology]

More than 20% of soft-tissue tumors belong to the group of adipocytic neoplasms. Difficulties may occur in the differential diagnosis of lipomas versus atypical lipomatous tumors/well-differentiated liposarcomas, in the distinction of dedifferentiated liposarcomas from other soft-tissue sarcoma entities and in the detailed subtyping of liposarcomas. Especially in biopsies, the correct diagnosis and grading may be hampered due to limited tissue. Because of the ever-increasing molecular-pathological knowledge of soft-tissue tumors and the rising distribution of molecular diagnostic assays in institutes of pathology, differential diagnosis has been facilitated, as more than 90% of adipocytic tumors carry more or less specific genomic alterations. In the following, the most important subtypes of adipocytic tumors are described morphologically and genomically.

TP53 in bone and soft tissue sarcomas

Genomic and functional study of existing and emerging sarcoma targets, such as fusion proteins, chromosomal aberrations, reduced tumor suppressor activity, and oncogenic drivers, is broadening our understanding of sarcomagenesis. Among these mechanisms, the tumor suppressor p53 (TP53) plays significant roles in the suppression of bone and soft tissue sarcoma progression. Although mutations in TP53 were thought to be relatively low in sarcomas, modern techniques including whole-genome sequencing have recently illuminated unappreciated alterations in TP53 in osteosarcoma. In addition, oncogenic gain-of-function activities of missense mutant p53 (mutp53) have been reported in sarcomas. Moreover, new targeting strategies for TP53 have been discovered: restoration of wild-type p53 (wtp53) activity through inhibition of TP53 negative regulators, reactivation of the wtp53 activity from mutp53, depletion of mutp53, and targeting of vulnerabilities in cells with TP53 deletions or mutations. These discoveries enable development of novel therapeutic strategies for therapy-resistant sarcomas. We have outlined nine bone and soft tissue sarcomas for which TP53 plays a crucial tumor suppressive role. These include osteosarcoma, Ewing sarcoma, chondrosarcoma, rhabdomyosarcoma (RMS), leiomyosarcoma (LMS), synovial sarcoma, liposarcoma (LPS), angiosarcoma, and undifferentiated pleomorphic sarcoma (UPS).

Update on Lipomatous Tumors with Emphasis on Emerging Entities, Unusual Anatomic Sites, and Variant Histologic Patterns

This article reviews the histologic patterns of spindle cell/pleomorphic lipoma, well-differentiated liposarcoma, and dedifferentiated liposarcoma in the context of both usual and atypical anatomic presentation. The utility of molecular and immunohistochemical diagnostic modalities to distinguish these entities is described. In addition, more recently described and controversial entities, including atypical spindle cell lipomatous tumor and anisometric cell lipoma, are discussed.

Pleomorphic Sarcomas: The State of the Art

This article focuses on pleomorphic sarcomas, which are malignant mesenchymal tumors with complex genetic background at the root of their morphologic pleomorphism. They are poorly differentiated tumors that may retain different lines of differentiation, sometimes correlating with clinicopathological or prognostic features. Accurate diagnosis in this group of tumors relies on adequate sampling due to their heterogeneity and assessment with both microscopy and large panels of immunohistochemistry. Molecular analyses have a limited role in their diagnosis as opposed to translocation-related sarcomas but may provide theranostic and important prognostic information in the future.

Molecular updates in adipocytic neoplasms✰

Adipocytic neoplasms include a diversity of both benign tumors (lipomas) and malignancies (liposarcomas), and each tumor type is characterized by its own unique molecular alterations driving tumorigenesis. Work over the past 30 years has established the diagnostic utility of several of these characteristic molecular alterations (e.g. MDM2 amplification in well- and dedifferentiated liposarcoma, FUS/EWSR1-DDIT3 gene fusions in myxoid liposarcoma, RB1 loss in spindle cell/pleomorphic lipoma). More recent studies have focused on additional molecular alterations which may have therapeutic or prognostic impact. This review will summarize several of the important molecular findings in adipocytic tumors that have been described over the past 10 years.

Subclassification of pleomorphic sarcomas: How and why should we care?

Pleomorphic sarcomas are a heterogeneous group of mesenchymal neoplasms with widely varied clinical behavior but overlapping histologic appearances. The following guidelines are helpful when approaching the diagnosis of a pleomorphic sarcoma. (1) Be aware of the relative incidence of the various sarcoma types: several pleomorphic sarcomas are relatively common (e.g., dedifferentiated liposarcoma and undifferentiated pleomorphic sarcoma), whereas others are exceptionally rare. (2) Pay attention to anatomic location: some pleomorphic sarcomas have a predilection for somatic soft tissues, especially the thigh (e.g., undifferentiated pleomorphic sarcoma, pleomorphic liposarcoma, pleomorphic rhabdomyosarcoma), whereas other pleomorphic sarcomas most often arise in the retroperitoneum (e.g., dedifferentiated liposarcoma). (3) Carefully sample the resection specimen, paying particular attention to areas with differences in gross appearances (e.g., fleshy, fibrous, mucoid, or gritty). (4) Search for histologic clues (i.e., myxoid stroma, lipoblasts, and osteoid matrix, in order to diagnose myxofibrosarcoma, pleomorphic liposarcoma, and extraskeletal osteosarcoma, respectively); these critical diagnostic features may be limited in extent. (5) Apply immunohistochemistry judiciously, after generating a differential diagnosis; always exclude metastatic sarcomatoid carcinoma and melanoma before diagnosing a pleomorphic sarcoma. This review will present an approach to the diagnosis of pleomorphic sarcomas, emphasizing differential diagnosis and the application of ancillary studies (immunohistochemistry and FISH), when relevant.

A rare case of dedifferentiated liposarcoma of the sinonasal cavity: A case report

Sarcoma is an uncommon histopathological presentation of sinonasal tumors, comprising ~15% of all cases; liposarcoma is particularly uncommon. An analysis of the available medical literature revealed no prior reports of dedifferentiated liposarcoma (DDLPS) of the sinonasal cavity. This case report presents a rare case of DDLPS of the sinonasal cavity. A 40-year old six-week pregnant female was admitted with a left nasal obstruction. Endoscopic evaluation of the left nasal cavity revealed a polypoid lesion. A computed tomography scan indicated a mass invading the left nasal cavity, maxillary sinus and anterior ethmoid sinus with focal destruction of the surrounding bone. A biopsy of the tumor was performed and hematoxylin and eosin staining of the tissue sections revealed proliferation of atypical and pleomorphic spindle cells with enlarged or elongated hyperchromatic nuclei and occasional vacuolated cytoplasm arranged in short interlacing fascicles or storiform structures, accompanied by tumor necrosis. These findings were consistent with undifferentiated pleomorphic sarcoma. Immunohistochemically, the tumor cells were positive for cyclin dependent kinase 4, mouse double minute 2 homolog (MDM2) and adipophilin. Fluorescence in situ hybridization (FISH) analysis revealed amplification of the MDM2 gene. Recently, undifferentiated pleomorphic sarcoma without areas of well-differentiated liposarcoma but with MDM2 amplification is regarded as conventional DDLPS. In the present case, the tumor was diagnosed as a DDLPS due to the results of histopathological, immunohistochemical and FISH analysis.

Comparison between retroperitoneal leiomyosarcoma and dedifferentiated liposarcoma

It is important to distinguish between leiomyosarcoma (LMS) and dedifferentiated liposarcoma (DDLS) in the retroperitoneum. The dedifferentiated component of DDLS shows an LMS-like morphology in some cases; thus, detailed evaluation is necessary to achieve an accurate diagnosis. Immunohistochemically, MDM2 and myogenic markers provide clues for the diagnoses. However, immunoreactivity for MDM2 and myogenic markers has not been well studied in retroperitoneal LMS and DDLS. Here, we compared the clinicopathological data of 20 retroperitoneal tumors initially diagnosed as LMS with that of 36 cases of retroperitoneal DDLS and conducted an immunohistochemical study. Four (20%) of the cases initially diagnosed as LMS were immunoreactive for MDM2. Fifteen cases (41.7%) of DDLS showed positive expression of two or more myogenic markers. The patients with LMS with MDM2 overexpression were older than the patients with LMS without MDM2 overexpression (P=0.0328). LMS with MDM2 overexpression showed a worse prognosis than DDLS (P=0.0408). No significant difference in prognosis was found between LMS without MDM2 overexpression and DDLS with myogenic differentiation. In conclusion, we recommend that systemic MDM2 expression analysis be performed in cases of retroperitoneal sarcoma. Overdependence on the expression of myogenic markers could lead to misdiagnosis in distinguishing LMS from DDLS.

HIF-1α, MDM2, CDK4, and p16 expression in ischemic fasciitis, focusing on its ischemic condition

Ischemic fasciitis is a benign myofibroblastic lesion, occurring in the sacral region or proximal thigh of elderly or bedridden individuals. The pathogenesis of ischemic fasciitis is thought to be based on ischemic condition; however, it has never been demonstrated. In this study, we examined the expression of ischemia-associated proteins in ischemic fasciitis by immunohistochemical and genetic methods. Specifically, this study aimed to reveal the expression of HIF-1α, MDM2, CDK4, p16, and gene amplification of MDM2 gene. Seven cases of ischemic fasciitis from among the soft-tissue tumors registered at our institution were retrieved. Histopathological findings were as follows: poorly demarcated nodular masses, a proliferation of spindle-shaped fibroblastic or myofibroblastic cells with oval nuclei and eosinophilic or pale cytoplasm, zonal fibrinous deposition, pseudocystic degeneration, granulation-like proliferation of capillary vessels, ganglion-like cells, myxoid or hyalinized stroma, and chronic inflammatory infiltration. Immunohistochemically, the spindle cells were positive for HIF-1α (7/7 cases), MDM2 (4/7 cases), CDK4 (4/7 cases), p16 (7/7 cases), p53 (2/7 case), cyclin D1 (7/7 cases), and alpha-smooth muscle actin (6/7 cases). Neither MDM2 gene amplification nor USP6 gene split signal was detected in any case. Overexpression of the above proteins may be associated with the pathogenic mechanism of ischemic fasciitis. It is noted that the immunohistochemical positivity of MDM2, CDK4, and p16 do not necessarily indicate malignant neoplasm such as dedifferentiated liposarcoma.

Hypothesis: The Intratumoral Immune Response against a Cancer Progenitor Cell Impacts the Development of Well-Differentiated versus Dedifferentiated Disease in Liposarcoma

Well-differentiated/dedifferentiated (WD/DD) liposarcoma is a rare malignancy of adipocyte origin (“fat cancer”). Tumors may be entirely WD, WD with a DD component, or rarely DD without a clear WD component. WD tumors are low grade and generally indolent, while tumors with a DD component are high grade and behave much more aggressively, with a modest potential for distant metastasis. The presence of cancer progenitor cells in WD/DD liposarcoma is suggested by clinical evidence and reported research findings. In addition, there are emerging data to support the existence of a naturally occurring, antigen-driven, and adaptive immune response within the tumor microenvironment. We hypothesize that the intratumoral immune response is directed against a cancer progenitor cell and that the outcome of this response impacts the development of WD versus DD disease. Further study will likely provide interesting insights into the disease biology of WD/DD liposarcoma that may be readily translated to other more common cancers.

Liposarcoma masquerading as an inflammatory pseudotumor: a case report

BACKGROUND

Distinguishing an atypical lipomatous tumor/well-differentiated liposarcoma from a benign lipomatous tumor on morphology alone can be difficult and there is an established role for MDM2 fluorescent in situ hybridization studies in making this differential diagnosis. There is no literature on the role for MDM2 fluorescent in situ hybridization studies in distinguishing between a well-differentiated liposarcoma with extreme fibrosis and a fibrosing inflammatory pseudotumor.

CASE PRESENTATION

We report the case of a 76-year-old Australian woman initially diagnosed by an excision biopsy with a retroperitoneal fibrosing inflammatory pseudotumor. She was then diagnosed 5 years later with a pleomorphic undifferentiated sarcoma. Upon review of the original resection specimen, we were able to show that the tumor demonstrated MDM2 amplification. MDM2 amplification was also present in some adjacent bland adipose tissue, and also in the tumor recurrence as a pleomorphic undifferentiated sarcoma.

CONCLUSION

Taken together, our findings provide strong evidence that the original tumor was a misdiagnosed well-differentiated liposarcoma with extreme fibrosis, and the pleomorphic undifferentiated sarcoma represented a recurrence of the same tumor with dedifferentiation.

Clinical effect of molecular methods in sarcoma diagnosis (GENSARC): a prospective, multicentre, observational study

BACKGROUND

Advances in molecular genetics of sarcoma have enabled the identification of type-specific aberrations. We aimed to assess the clinical effect of systematic implementation of molecular assays to improve sarcoma misdiagnosis.

METHODS

In this multicentre, observational study, we recruited patients from 32 centres of the French Sarcoma Group/Reference Network in Pathology of Sarcomas. Eligibility criteria included: biopsy or surgical resection; suspicion of: dermatofibrosarcoma protuberans (cohort 1), dedifferentiated liposarcoma (cohort 2), Ewing's sarcoma family of tumours (cohort 3), synovial sarcoma (cohort 4), alveolar rhabdomyosarcoma (cohort 5), and myxoid or round cell liposarcoma (cohort 6); review by one sarcoma-expert pathologist; availability of frozen material (except for cohort 1 of patients with dermatofibrosarcoma protuberans because anti-CD34 immunohistochemistry is performed on paraffin-embedded tissue); and patient information. For each case, the pathologist made one primary diagnosis followed by up to two differential diagnoses, based on histological characteristics only. Each diagnosis was classified as certain, probable, or possible. For each case to determine the molecular classification, we did fluorescence in-situ hybridisation on paraffin-embedded samples. We also did comparative genomic hybridisation and quantitative PCR (cohort 2) or reverse transcriptase PCR (cohorts 3-6) on frozen and paraffin-embedded samples. We made a final diagnosis based on the molecular results. The clinical effect of diagnosis correction was assessed by a board of experts.

FINDING

Between June 22, 2009, and Oct 30, 2012, 395 patients were enrolled in the study, of which 384 were eligible for inclusion. The diagnosis was eventually modified by molecular genetics for 53 patients: eight (16%) of 50 patients with dermatofibrosarcoma (cohort 1), seven (23%) of 30 patients with dedifferentiated liposarcoma (cohort 2), 13 (12%) of 112 with Ewing's sarcoma family of tumours (cohort 3), 16 (16%) of 97 patients with synovial sarcoma (cohort 4), seven (15%) of 46 patients with alveolar rhabdomyosarcoma (cohort 5), and two (4%) of 49 patients with myxoid or round cell liposarcoma (cohort 6), with an effect on primary management or prognosis assessment in 45 cases.

INTERPRETATION

Molecular genetic testing should be mandatory for diagnostic accuracy of sarcoma and appropriate clinical management, even when histological diagnosis is made by pathologist experts in this field.

FUNDING

French National Cancer Institute and Nice University Hospital.

Elevated expression of HSP90 and the antitumor effect of an HSP90 inhibitor via inactivation of the Akt/mTOR pathway in undifferentiated pleomorphic sarcoma

BACKGROUND

Undifferentiated pleomorphic sarcoma (UPS) is a heterogeneous tumor group, and little is known about molecular target therapy for UPS. Heat shock protein 90 (HSP90) is an expressed chaperone that refolds certain denatured proteins under stress conditions. One of these proteins is Akt. The disruption of Akt signaling plays an important role in tumor progression. The present study's purpose was to analyze the HSP90 expression, Akt/mTOR pathway activation and the correlation between HSP90 expression and its pathway activation in UPS.

METHODS

The status of HSP90 and the profiles of the Akt/ mTOR pathway were assessed by immunohistochemistry in 79 samples of UPS, and these data were compared with clinicopathological and histopathological findings. The expressions of indicated proteins were assessed by Western blotting in five frozen samples. After treating UPS cells with the HSP90 inhibitor, we assessed the antitumor effect of the inhibitor.

RESULTS

Immunohistochemically, phosphorylated Akt (p-Akt), p-mTOR, p-S6RP and p-4EBP were positive in 57.3, 51.9, 54.5 and 57.1% of the UPS samples, respectively. The expressions of those phosphorylated proteins were correlated with each other. HSP90 expression was elevated in 56.4% of the samples and was correlated with p-Akt, p-mTOR and p-S6RP. The immunohistochemical results were confirmed by Western blotting. The HSP90 inhibitor led to decreased viability and invasiveness of the cells and inactivated the AKT/mTOR pathway in vitro.

CONCLUSION

Elevated expression of HSP90 is a poor-prognosis factor and is involved in the activation of the Akt/mTOR pathway in UPS. HSP90 inhibition is a potential treatment option for UPS.

Fluorescence In Situ Hybridization for MDM2 Amplification as a Routine Ancillary Diagnostic Tool for Suspected Well-Differentiated and Dedifferentiated Liposarcomas: Experience at a Tertiary Center

Background. The assessment of MDM2 gene amplification by fluorescence in situ hybridization (FISH) has become a routine ancillary tool for diagnosing atypical lipomatous tumor (ALT)/well-differentiated liposarcoma and dedifferentiated liposarcoma (WDL/DDL) in specialist sarcoma units. We describe our experience of its utility at our tertiary institute. Methods. All routine histology samples in which MDM2 amplification was assessed with FISH over a 2-year period were included, and FISH results were correlated with clinical and histologic findings. Results. 365 samples from 347 patients had FISH for MDM2 gene amplification. 170 were positive (i.e., showed MDM2 gene amplification), 192 were negative, and 3 were technically unsatisfactory. There were 122 histologically benign cases showing a histology:FISH concordance rate of 92.6%, 142 WDL/DDL (concordance 96.5%), and 34 cases histologically equivocal for WDL (concordance 50%). Of 64 spindle cell/pleomorphic neoplasms (in which DDL was a differential diagnosis), 21.9% showed MDM2 amplification. Of the cases with discrepant histology and FISH, all but 3 had diagnoses amended following FISH results. For discrepancies of benign histology but positive FISH, lesions were on average larger, more frequently in "classical" (intra-abdominal or inguinal) sites for WDL/DDL and more frequently core biopsies. Discrepancies of malignant histology but negative FISH were smaller, less frequently in "classical" sites but again more frequently core biopsies. Conclusions. FISH has a high correlation rate with histology for cases with firm histologic diagnoses of lipoma or WDL/DDL. It is a useful ancillary diagnostic tool in histologically equivocal cases, particularly in WDL lacking significant histologic atypia or DDL without corresponding WDL component, especially in larger tumors, those from intra-abdominal or inguinal sites or core biopsies. There is a significant group of well-differentiated adipocytic neoplasms which are difficult to diagnose on morphology alone, in which FISH for MDM2 amplification is diagnostically contributory.