MDM2 and CDK4 Immunohistochemistry: Should It Be Used in Problematic Differentiated Lipomatous Tumors?: A New Perspective

Butterfly-Shaped Epicardial Lipoma of the Heart

Cardiac tumors are a rare entity with typically unspecific symptoms. We present the case of a 43-year old female patient with epigastric pain and palpitations with a long history of diagnostics prior to discovery of an epicardial mass. The epicardial tumor with arterial vascularization from the left anterior descending artery was resected in a beating heart procedure and was found to be a lipomatous soft tissue tumor. A lack of mouse double minute 2 gene amplification in fluorescent in situ hybridization confirmed the diagnosis of a benign cardiac lipoma. Resection led to a long-term resolution of symptoms.

Overdiagnosis of atypical lipomatous tumors/well-differentiated liposarcomas by morphological diagnosis using only HE stained specimens: a case-control study with MDM2/CDK4 immunostaining and MDM2/CDK4 fluorescence in situ hybridization

BACKGROUND

Lipomatous tumors represent the most common type of soft tissue neoplasms. Mouse double minute 2 homolog (MDM2)/cyclin-dependent kinase 4 (CDK4) immunostaining is considered effective in differentiating between benign lipomas and intermediate malignant atypical lipomatous tumors/well-differentiated liposarcomas (ALT/WDLPSs). However, these tumors have traditionally been diagnosed histopathologically using hematoxylin and eosin-stained specimens, which is referred to here as morphological diagnosis. In this study, the accuracy of morphological diagnoses that had been made before MDM2/CDK4 immunostaining became available for distinguishing between lipoma and ALT/WDLPS was examined.

METHODS

The study participants were 109 patients with a morphological diagnosis of lipoma (68 patients) or ALT/WDLPS (41 patients) who had undergone surgical resection of the tumor in our hospital between 2009 and 2012. Tissue samples from all patients were used for MDM2/CDK4 immunostaining and the confirmation of MDM2/CDK4 amplification by fluorescence in situ hybridization (FISH).

RESULTS

Of the 41 patients with a morphological diagnosis of ALT/WDLPS, only 17 were positive for MDM2 FISH. In addition, one of the 68 patients with a morphological diagnosis of lipoma showed MDM2 amplification by FISH. When the definitive diagnosis of ALT/WDLPS was made by the positive results of MDM2 FISH, the sensitivity and specificity of morphological diagnosis were 41.5% and 98.5%, respectively. The sensitivity of MDM2 and CDK4 immunostaining was 55.6% and 40.0%, respectively, and their specificity was 87.0% and 84.6%, respectively. This indicates that the diagnostic accuracy of these immunostaining assays was not particularly high. The clinical features suggesting ALT/WDLPS were: patient age (older), maximum tumor diameter (large, cut-off value of 125 mm), tumor location (lower limb), and tumor depth (deep-seated).

CONCLUSIONS

Morphological diagnosis alone can accurately diagnose lipomas. However, it has a propensity to overdiagnose ALT/WDLPS. Thus, MDM2 FISH should be used more proactively, not only for lesions with obvious morphological abnormalities, but also for lipomatous tumors that are clinically suggestive of ALT/WDLPS.

Efficacy of surgery in the management of multiple recurrences of retroperitoneal dedifferentiated liposarcoma

BACKGROUND

Retroperitoneal dedifferentiated liposarcoma is associated with a high risk of recurrence; however, treatment strategies that are more effective than surgery remain to be established. This study aimed to determine the optimal number of surgeries that would be effective for patients with recurrent disease. Furthermore, the improvement in prognosis was evaluated according to the malignancy level.

METHODS

The effect of each type of surgery on the prognosis of 118 patients with retroperitoneal dedifferentiated liposarcoma treated at the Osaka International Cancer Institute between 1997 and 2022 was investigated. Among the 118 patients, 103 underwent initial surgery, while 54 and 30 patients underwent second and third surgeries, respectively. The overall and disease-free survival rates of each group were compared using the Kaplan-Meier method, and the log-rank test was used to determine statistical significance in univariate analysis. 18F-Fluorodeoxyglucose Positron Emission Tomography (FDG-PET) was used to assess malignancy. Maximum standardized uptake values (SUVmax) of ≥ 4 and < 4 were classified as high and low malignancy, respectively.

RESULTS

The first and second surgeries resulted in a significant improvement in the overall survival rate, regardless of the malignancy level (p < 0.001); however, no significant improvement in prognosis was observed after the third surgery (p = 0.077). Low-grade malignancies are associated with a better postoperative prognosis, even in cases of recurrence. In contrast, high-grade malignancies exhibit a reduction in surgical efficacy.

CONCLUSIONS

This study highlights the importance of considering the tumor malignancy level and the patient's overall condition when deciding whether to perform repeated surgical interventions. Surgical treatment can prolong overall survival, even in patients with recurrence; however, it is advisable to assess malignancy levels when determining the suitability of surgery beyond the second recurrence.

Atypical lipomatous tumor/well differentiated liposarcoma and related mimics with updates. When is molecular testing most cost-effective, necessary, and indicated?

The classification and work-up of adipocytic neoplasms remains challenging and sometimes controversial. Since its initial description by Dr. Enterline, the variety of subtypes and morphological appearances considered to represent the spectrum of atypical lipomatous tumor/well differentiated liposarcoma (ALT/WDL) has expanded, resulting in significant morphologic overlap with other entities, including the recently described atypical spindle cell/pleomorphic lipomatous tumor (ASPLT), conventional spindle cell/pleomorphic lipoma (SPL), and so-called "low-grade" forms of dedifferentiated liposarcoma (DL). Nevertheless, the distinction of most examples of ALT/WDL from lipomas/lipoma-like lesions is easily performed on routine histologic examination but can be problematic if the characteristic atypical cells are poorly represented, particularly in small biopsy specimens, obscured by other cellular elements (inflammation), or simply not recognized. The discovery that lipomatous tumors harbor specific and unique karyotypes and molecular events has resulted in ancillary tests that can help provide more accurate diagnoses, especially in less-than-optimal scenarios. Confirmation of MDM2 immunohistochemical over-expression and detection of the MDM2 gene rearrangement via fluorescent in situ hybridization (FISH) have proven particularly reliable and useful. While FISH analysis for MDM2 gene amplification may be helpful for confirming (or excluding) ALT/WDL, it also can lead to overutilization and overdependence. Furthermore, a small subset of otherwise typical ALT/WDL lack MDM2 gene amplification, employing alternative molecular pathways. The recent recognition of ASPLT has introduced a tumor easily mistaken morphologically for ALT/WDL, often exhibiting bizarre and pleomorphic lipoblasts, but lacking the underlying molecular abnormalities and subsequent risk of dedifferentiation. ASPLT also have overlapping features with the better-established SPL but with a greater tendency to locally recur and more frequent involvement of the distal extremities. The precise criteria separating cellular forms of ALT from what some consider "low grade" forms of DL remains controversial and inconsistently applied, even among individual pathologists within institutions. Given their underlying shared cytogenetic abnormality, molecular testing has no utility in this distinction. Herein is a comprehensive historical overview of ALT/WDL, with updates on its distinction from other similar lipomatous tumors and DL, including practical evidence-based criteria for the appropriate cost-effective use of MDM2 testing.

MDM2 FISH testing criteria in adipose tissue tumors with mature adipocytic morphology - A resection case-based study

The current criteria for utilizing MDM2 Fluorescence In Situ Hybridization (FISH) in adipose-derived tumors were first introduced in 2015 and have been widely adopted. However, these criteria may fail to identify some atypical lipomatous tumors / well-differentiated liposarcoma (ALT/WDL) with mature adipocytic morphology in clinical practice, possibly due to the fact that the existing criteria are primarily based on biopsy cases. Hence, a criterion based on resection cases is needed. In this study, we included 87 adipose tissue tumors with mature adipocytic morphology which were first resected, as well as 9 consultation cases and 25 recurrent resection cases. The final diagnosis was based on MDM2 amplification status. Among the 87 first-time resection cohort, MDM2 FISH amplification was observed in only 2 (5%) of the 39 superficial cases. Marginal infiltration was significantly different in both the MDM2 FISH negative and positive groups (p < 0.05). Of the 37 intramuscular tumors, 17 (46%) showed MDM2 FISH amplification. The MDM2 amplification positive group had a larger tumor size than MDM2 amplification negative group (p = 0.042). Tumors of larger size (≥11 cm) were highly correlated with MDM2 amplification (p = 0.003), but still, 35.3% of the MDM2 amplification-positive cases had tumor sizes less than 11 cm. Eight (66.7%) out of twelve retroperitoneal/ pelvic cases were MDM2 FISH positive. Among the 25 recurrent cases, twenty (80%) of them had MDM2 FISH amplification. In conclusion, we recommend MDM2 FISH for: 1. superficial cases with marginal infiltration based on adequate margin sampling; 2. all intramuscular tumors, retroperitoneal/pelvic tumors and recurrent tumors, both in resection cases and biopsy cases.

Utility of Retrospective Molecular Analysis in Diagnostically Challenging Mesenchymal Neoplasms

Introduction: Molecular analysis plays a growing role in the diagnosis of mesenchymal neoplasms. The aim of this study was to retrospectively apply broad, multiplex molecular assays (a solid tumor targeted next-generation sequencing [NGS]) assay and single nucleotide polymorphism [SNP] microarray) to selected tumors, exploring the current utility and limitations. Methods: We searched our database (2010-2020) for diagnostically challenging mesenchymal neoplasms. After histologic review of available slides, tissue blocks were selected for NGS, SNP microarray, or both. DNA and RNA were extracted using the AllPrep DNA/RNA FFPE Kit Protocol on the QIAcube instrument. The NGS platform used was the TruSight Tumor 170 (TST-170). For SNP array, copy number variant (CNV) analysis was performed using the OncoScanTM CNV Plus Assay. Results: DNA/RNA was successfully extracted from 50% of tumors (n = 10/20). Specimens not successfully extracted included 6 core biopsies, 3 incisional biopsies, and 1 resection; 4 were decalcified (3 hydrochloric acid, 1 ethylenediaminetetraacetic acid). Higher tumor proportion and number of tumor cells were parameters positively associated with sufficient DNA/RNA extraction whereas necrosis and decalcification were negatively associated with sufficient extraction. Molecular testing helped reach a definitive diagnosis in 50% of tumors (n = 5/10). Conclusions: Although the overall utility of this approach is limited, these molecular panels can be helpful in detecting a specific "driver" alteration.

The value of a new diagnostic strategy for adipocytic soft tissue tumors in adults: A retrospective study

INTRODUCTION

The distinction between lipoma and well-differentiated liposarcoma (WDLPS), or "atypical lipomatous tumor" (ALT), is crucial as it impacts patient management. A group of European experts led by Benjamin Moulin recently issued a consensus report to define the role of radiology in managing these lesions. It describes an algorithm defining the criteria prompting a diagnostic biopsy of deep lipomatous tumors of the limbs and chest wall. The primary aim of this study was to evaluate the algorithm's diagnostic performance.

MATERIALS AND METHODS

Between 2012 and 2019, all biopsies of deep fatty tumors of the limbs or chest wall with a pre-biopsy MRI assessment were recorded at our institution. The MRI scans were reviewed by two radiologists. Each lesion was classified according to biopsy status by applying the algorithm of the European panel. The algorithm's diagnostic performance was assessed by calculating the sensitivity, specificity, positive predictive value and negative predictive value. Inter-rater agreement was also assessed.

RESULTS

Of the 156 tumors in our study, 148 (94.9%) required a biopsy, and the algorithm's sensitivity for detecting ALT/WDLPS was 100% with specificity of 6.3% and a PPV of 20.3%. Inter-rater agreement was almost perfect with a kappa value of 0.882.

CONCLUSION

The European algorithm demonstrates perfect sensitivity, an important criterion for a screening examination such as MRI in this setting. The algorithm's low specificity, however, emphasizes the need for further studies to redefine the optimum size cut-off value, especially for lesions without atypical criteria or an anatomical location at risk of post-surgical recurrence.

New developments in the pathology and molecular biology of retroperitoneal sarcomas

Retroperitoneal sarcomas (RPS) refer to a heterogeneous group of malignancies of mesenchymal origin developing from retroperitoneal tissues and vessels. The most frequent RPS are well differentiated/dedifferentiated liposarcomas and leiomyosarcomas, but other rare histological subtypes can be observed. Over the last decade, significant advances have been made in the pathological and molecular characterization of sarcomas. These advances have led to major changes in their diagnostic management as well as in the development of new therapeutic strategies based on tumor biology and microenvironment. This review describes the current knowledge and recent findings in the pathology and molecular biology of the most frequent RPS subtypes.

Application of immunohistochemical studies in diagnosing emerging superficial mesenchymal neoplasms

Molecular diagnostics, with the subsequent development of novel immunohistochemical markers, continues to advance and expand the field of soft tissue pathology. As such, the ever-evolving molecular diagnostic landscape will continue to shape and refine our understanding and classification of neoplasms. This article reviews the current literature on various tumors of mesenchymal origin, including fibroblastic/fibrohistiocytic, adipocytic, vascular, and tumors of uncertain origin. We aim to give the reader a detailed understanding and pragmatic approach to various new and established immunohistochemical stains in diagnosing these neoplasms and also discuss various pitfalls with significant repercussions.

MDM2 for the practicing pathologist: a primer

The mouse double minute 2 (MDM2) gene is located on the long arm of chromosome 12 and is the primary negative regulator of p53. The MDM2 gene encodes an E3 ubiquitin-protein ligase that mediates the ubiquitination of p53, leading to its degradation. MDM2 enhances tumour formation by inactivating the p53 tumour suppressor protein. The MDM2 gene also has many p53-independent functions. Alterations of MDM2 may occur through various mechanisms and contribute to the pathogenesis of many human tumours and some non-neoplastic diseases. Detection of MDM2 amplification is used in the clinical practice setting to help diagnose multiple tumour types, including lipomatous neoplasms, low-grade osteosarcomas and intimal sarcoma, among others. It is generally a marker of adverse prognosis, and MDM2-targeted therapies are currently in clinical trials. This article provides a concise overview of the MDM2 gene and discusses practical diagnostic applications pertaining to human tumour biology.

Silver In Situ Hybridization for the Rapid Assessment of MDM2 Amplification in Soft Tissue and Bone Tumors. Validation Based on an Audit of 192 Consecutive Cases Evaluated by Silver In Situ Hybridization and Fluorescence In Situ Hybridization

The discovery of almost invariable mouse double minute 2 (MDM2) amplification among atypical lipomatous tumors (ALT)/well-differentiated liposarcoma and dedifferentiated liposarcoma is incorporated into the contemporary diagnostic workup of fatty lesions. MDM2 amplifications are also found frequently in intimal sarcomas and in low-grade osteogenic sarcoma. At present, fluorescence in situ hybridization (FISH) is the reference test for MDM2 assessment. We are interested in evaluating silver in situ hybridization (SISH) for this purpose. Between October 2016 and May 2020, in 192 consecutive cases requiring MDM2 FISH, SISH was also performed concurrently, including 77 (40.1%) core biopsies and 115 (58.9%) surgical specimens. The mean patient age was 61.0 years. SISH results were available overnight or within 48 hours if repeat testing was required. FISH results were available within 2 to 5 weeks. The cost of SISH was one third of FISH. FISH demonstrated MDM2 amplification in 44 cases (23.6%), was negative in 144 cases (74.4%) and nondiagnostic in 4 decalcified cases (2.0%). SISH showed MDM2 amplification in 33 cases (17.2%), no amplification in 119 cases (62.0%), and indeterminate results because of poor signal in 40 (20.8%) cases. All 33 (100%) SISH-amplified tumors and 113 of 119 (95.0%) nonamplified results were confirmed by FISH. There were no clear differences in the performance of SISH on NCB versus surgical specimens. The overall performance indices of SISH are sensitivity 75%, specificity 78.5%, positive predictive value 100%, and negative predictive value 95.8%. FISH is not required when SISH is clearly amplified. This is clinically useful and improves efficiency. Nonamplified SISH results provide early indications of the likely FISH findings, but there is a 4.2% chance of FISH being positive. At present, the main drawback of SISH is the high rate of nondiagnostic tests. Optimization of SISH signal detection to reduce the proportion of indeterminate results is our current focus.

Molecular testing of soft tissue tumors

BACKGROUND

The diagnosis of soft tissue tumors is challenging, especially when the evaluable material procured is limited. As a result, diagnostic ancillary testing is frequently needed. Moreover, there is a trend in soft tissue pathology toward increasing use of molecular results for tumor classification and prognostication. Hence, diagnosing newer tumor entities such as CIC-rearranged sarcoma explicitly requires molecular testing. Molecular testing can be accomplished by in situ hybridization, polymerase chain reaction, as well as next generation sequencing, and more recently such testing can even be accomplished leveraging an immunohistochemical proxy.

CONCLUSION

This review evaluates the role of different molecular tests in characterizing soft tissue tumors belonging to various cytomorphologic categories that have been sampled by small biopsy and cytologic techniques.

Intraoral lipoma with degenerative changes mimicking atypical lipomatous tumor: an immunohistochemical study

Lipomas are mesenchymal neoplasms relatively uncommon in the oral cavity. Lipomas can exhibit histopathological features mimicking atypical lipomatous tumors (ALT) or dysplastic lipoma (DL) in the presence of degenerative changes. Relevantly, immunohistochemistry assists in the correct diagnosis. Herein, we present the case of a 54-year-old male with a sessile nodule located on the dorsum of the tongue. The histopathological analysis showed a diffuse, non-circumscribed adipocytic proliferation constituted by cells of variable size containing cytoplasmic vacuoles and displaced nuclei, some resembling lipoblasts supported by fibrous connective tissue stroma. By immunohistochemistry, tumor cells were positive for vimentin, S100, FASN, CD10, and p16. Rb expression was intact. Moreover, CD34, p53, MDM2, and CDK4 were negative. After 2-year of follow-up, no alteration or recurrence was observed. In conclusion, MDM2, CDK4, p53, and Rb immunomarkers can be used reliably to differentiate benign lipoma with degenerative changes from ALT and DL.

Updates in Pathology for Retroperitoneal Soft Tissue Sarcoma

Retroperitoneal tumors are extremely rare. More than 70% of primary retroperitoneal soft tissue tumors are malignant. The most common sarcomas in the retroperitoneum include liposarcomas and leiomyosarcoma, however other sarcomas, along with benign mesenchymal tumors, can occur. Sarcomas are a heterogenous group of tumors with overlapping microscopic features, posing a diagnostic challenge for the pathologist. Correct tumor classification has become important for prognostication and the evolving targeted therapies for sarcoma subtypes. In this review, the pathology of retroperitoneal soft tissue sarcomas is discussed, which is important to the surgical oncologist. In addition, less common sarcomas and benign mesenchymal tumors of the retroperitoneum, which may mimic sarcoma clinically and pathologically, are also discussed.

Paraplegia due to spinal epidural lipoma without spinal dysraphism in an adolescent patient: a case report

We report the case of a rare lipoma arising in the epidural space of a 14-year-old boy without spinal dysraphism. Lipomas are rare in pediatric soft tissue tumors, accounting for only about 4% of cases. The incidence of an intraspinal epidural lipoma without spinal dysraphism is extremely rare in pediatric patients. In this case, the patient had progressive motor deficits in the lower extremities and difficulty in urination and defecation. Magnetic resonance imaging showed an extradural tumor compressing the spinal cord at the T3-T7 level. Because of the progressive neurological deficits, we performed an emergency surgery. The tumor was completely resected en bloc, and histopathology revealed mature adipose tissue with fibrous septa, diagnosed as atypical lipomatous tumor / well-differentiated liposarcoma. The patient fully recovered and there was no tumor recurrence for 6 years since the surgery. However, re-examination using fluorescence in situ hybridization after 6 years of surgery changed the diagnosis to lipoma as no amplification of murine double-minute type 2 oncogene was observed. In liposarcoma, histopathological diagnosis using fluorescence in situ hybridization is mandatory. Our case illustrates that immunohistochemical diagnosis alone can be misleading. Hence, prompt surgery is required for progressive neuropathy.

MicroRNAs as Potential Biomarkers in the Differential Diagnosis of Lipomatous Tumors and Their Mimics

Adipocytic tumors are the most common subtype of soft tissue tumors. In current clinical practice, distinguishing benign lipomas from well-differentiated liposarcomas (WDLPS), as well as dedifferentiated liposarcomas (DDLPS) from their morphologic mimics, remains a significant diagnostic challenge. This is especially so when examining small biopsy samples and without the aid of additional ancillary tests. Recognizing the important role that microRNAs (miRNAs) play in tumorigenesis and their potential utility in tumor classification, we analyzed routine clinical tissue samples of benign and malignant lipomatous tumors, as well as other sarcoma mimics, to identify distinguishing miRNA-based signatures that can aid in the differential diagnosis of these entities. We discovered a 6-miRNA signature that separated lipomas from WDLPS with high confidence (AUC of 0.963), as well as a separate 6-miRNA signature that distinguished DDLPS from their more aggressive histologic mimics (AUC of 0.740). Functional enrichment analysis unveiled possible mechanistic involvement of these predictive miRNAs in adipocytic cancer-related biological processes and pathways such as PI3K/AKT/mTOR and MAPK signaling, further supporting the relevance of these miRNAs as biomarkers for adipocytic tumors. Our results demonstrate that miRNA expression profiling may potentially be used as an adjunctive tool for the diagnosis of benign and malignant adipocytic tumors. Further validation studies are warranted.

Differential diagnosis of lipoma and atypical lipomatous tumor/well-differentiated liposarcoma by cytological analysis

BACKGROUND

Adipocytic tumors are the most common soft tissue tumors, with lipomas and atypical lipomatous tumor/well-differentiated liposarcomas (ALT/WDL), which comprise most cases. Preoperative differential diagnosis of lipoma or ALT/WDL can provide important information for decisions regarding treatment. We evaluated the cytological findings of 20 cases of lipoma and ALT/WDL.

METHODS

Fluorescence in situ hybridization (FISH) was performed on formalin-fixed paraffin-embedded specimens (FFPE) to examine mouse double minute 2 homolog (MDM2) amplification in all cases. Tissue samples were collected from the center of the surgical materials, stained with Pap, and evaluated for 12 cytological parameters by six cytotechnologists.

RESULTS

The findings regarding large atypical cells, multinucleated cells, and nuclear pleomorphism were highly concordant among the cytotechnologists and were associated with MDM2 amplification. Large atypical cells, considered a highly specific feature of ALT/WDL, were not observed in lipoma cases. However, the sensitivity of the large atypical cell findings was not high (67%); therefore, comprehensive evaluation of multinucleated cells and pleomorphism is crucial for predicting ALT/WDL diagnosis. FISH of MDM2 on Pap-stained specimens was performed in four cases. In two, the results were similar to those of MDM2 FISH performed on FFPE sections and were reproducible, whereas in the other two, the signal could not be evaluated because of the strong background coloration.

CONCLUSIONS

Cytology specimens may be useful for the preoperative diagnosis of adipocytic tumors, particularly if the FISH conditions for Pap-stained specimens and the detection accuracy of MDM2 amplification can be improved.

Expression of FRS2 in atypical lipomatous tumor/well-differentiated liposarcoma and dedifferentiated liposarcoma: an immunohistochemical analysis of 182 cases with genetic data

Background

The fibroblast growth factor receptor substrate 2 (FRS2) gene is located close to MDM2 and CDK4 within the 12q13-15 chromosomal region. FRS2 gene was recently found to be consistently amplified in atypical lipomatous tumor (ALT)/well-differentiated liposarcoma (WDL) and dedifferentiated liposarcoma (DDL), suggesting the detection of FRS2 amplification could be a diagnostic tool for ALT/WDL/DDLs. However, the expression of FRS2 protein and diagnostic value of FRS2 immunohistochemistry (IHC) has not been evaluated in a large cohort of ALT/WDL/DDLs.

Methods

A SNOMED search of hospital surgical pathology files from January 2007 to July 2020 identified 182 ALT/WDL/DDLs with available materials. FRS2 fluorescence in situ hybridization (FISH) and IHC were performed on 182 ALT/WDL/DDLs and 64 control samples. The expression of FRS2 was also compared with that of classic immunomarkers (MDM2 and CDK4) of this tumor entity.

Results

This study included 91 ALT/WDLs and 91 DDLs. The FISH results showed 172 of 182 (94.5%) cases were FRS2-amplified, and 10 cases were FRS2-nonamplified. Immunostaining results showed 171 (94.0%) ALT/WDL/DDLs were positive for FRS2 and 11 cases (6.0%) were FRS2-immunonegative. In 172 FRS2-amplified cases, 166 (96.5%) were FRS2-immunopositive, and 6 (3.5%) were negative. Among 10 FRS2-nonamplified ALT/WDL/DDL cases, 5 cases were FRS2-immunonegative, and 5 tumors displayed 1+ staining for this marker. In 64 control cases, none of them exhibited FRS2 amplification. Forty-seven (73.5%) control cases were negative for FRS2 immunostaining, while 17 cases (26.5%) were FRS2-immunopositive. Fifteen of these false positive samples (15/17, 88.2%) showed 1+ positivity and only 2 cases (2/17, 11.8%) displayed 2+ positivity. In ALT/WDL/DDLs, the sensitivity of FRS2 immunostaining was slightly lower than MDM2 (FRS2 vs. MDM2: 94.0% vs 100.0%) and CDK4 (FRS2 vs. CDK4: 94.0% vs 97.0%). However, the specificity of FRS2 (73.5%) was slightly higher than that of MDM2 (67.8%) and CDK4 (64.4%).

Conclusion

This study indicated that FRS2 IHC had relatively good consistency with FRS2 FISH, suggesting that FRS2 immunostaining could be utilized as an additional screening tool for the diagnosis of ALT/WDL/DDL. It must be emphasized that MDM2/CDK4/FRS2 especially MDM2 FISH remains the gold standard and the most recommended method to diagnose this entity.

Lessons learnt from MDM2 fluorescence in-situ hybridisation analysis of 439 mature lipomatous lesions with an emphasis on atypical lipomatous tumour/well-differentiated liposarcoma lacking cytological atypia

AIMS

Amplification of the murine double minute-2 (MDM2) gene, which is usually detected with fluorescence in-situ hybridisation (FISH), is the key driving event for atypical lipomatous tumours (ALTs)/well-differentiated liposarcomas (WDLs). We sought to determine the concordance between the histopathological findings and MDM2 FISH in the diagnosis of ALT/WDL, and to identify the histological features of MDM2-amplified tumours lacking classic atypia.

METHODS AND RESULTS

We performed a retrospective analysis of all mature lipomatous lesions subjected to MDM2 FISH analysis at our institution. MDM2 FISH analysis was performed on 439 mature lipomatous lesions: 364 (82.9%) were negative and 75 (17%) were positive. In 17 of 75 (22.6%) ALTs/WDLs, cytological atypia was not identified on initial histological assessment, thus favouring lipoma. On review, these cases shared common histological features, consisting of a very low number of relatively small stromal cells within the tumour lobules, with mildly coarse chromatin and oval nuclei, admixed with unremarkable adipocytes in a tumour background devoid of fibroconnective septa, areas of fibrosis, or blood vessels. These cells matched the cells in which FISH showed MDM2 amplification. In contrast, 13 cases (3.5%) regarded as suspicious for ALT/WDL on the basis of histology lacked MDM2 amplification and were reclassified following the FISH findings.

CONCLUSIONS

We conclude that a subset of lipoma-like ALTs/WDLs are not associated with any of the features typically described in ALT/WDL. Our study also showed that tumours >100 mm are more likely to be ALT/WDL; however, a history of recurrence or concerning clinical/radiological features was not significantly associated with classification as ALT/WDL.

Mesenchymal Tumors of the Mediastinum: An Update on Diagnostic Approach

Mesenchymal tumors of the mediastinum are a heterogenous group of rare tumors with divergent lineages. Mediastinal mesenchymal tumors are diagnostically challenging due to their diversity and morphologic overlap with nonmesenchymal lesions arising in the mediastinum. Accurate histologic diagnosis is critical for appropriate patient management and prognostication. Many mediastinal mesenchymal tumors affect distinct age groups or occur at specific mediastinal compartments. Neurogenic tumors, liposarcoma, solitary fibrous tumor, and synovial sarcoma are common mesenchymal tumors in the mediastinum. Herein, we provide an update on the diagnostic approach to mediastinal mesenchymal tumors and a review of the histologic features and differential diagnosis of common benign and malignant mesenchymal tumors of the mediastinum.

Benign but Terminal: Cardiopulmonary Collapse from a Massive Chest Wall Lipoma

Lipomas are the most common benign soft tissue tumor. Yet, strikingly simple tumors can become problematic when compounded by odd characteristics such as size and location. We report the case of a 53-year-old male who developed complete right lung collapse secondary to a large right-sided chest wall lipoma with accelerated growth in the past 6 months. Bronchoscopy revealed extrinsic compression of the right mainstem bronchus. Histopathology of the soft tissue mass was suggestive of a lipoma. The mass was not amenable to surgery due to a high risk of mortality from his underlying comorbidities. His hospital stay was complicated by progressive end-stage restrictive lung disease necessitating intubation and eventually a tracheostomy, recurrent pneumonias, multiorgan dysfunction, and his eventual demise. We highlight a rare presentation of an unchecked lipoma, which ultimately led to the death of our patient. Simple lipomas show insidious growth and can remain asymptomatic until they reach a large size. Chest wall tumors should be considered malignant until proven otherwise by excisional biopsy. This reiterates the need to treat all chest wall tumors with wide resection in order to provide the best chance for cure.

Resection of a giant retroperitoneal lipoma herniating through the inguinal canal

Retroperitoneal lipomas are extremely rare with few cases reported so far in the literature. They can reach different sizes and present with a variety of symptoms. The differential diagnosis is mainly with well-differentiated liposarcoma (WDLPS). We present a 34-year-old woman with a retroperitoneal lipoma herniating through the inguinal canal into the proximal thigh. The patient underwent complete oncological resection using a Karakousis's abdominoinguinal incision. Retroperitoneal lipomas are a very rare condition and sometimes require resections technically challenging. MDM2 amplification is critical for its differential diagnosis with WDLPS.

Recent Advancement in Atypical Lipomatous Tumor Research

After Evans and colleagues identified the lipomatous tumor with a well-differentiated liposarcoma in a subcutaneous location or within a muscle layer, namely, atypical lipomatous tumor (ALT), this malignancy has been investigated to clarify the characteristics of clinical behavior and genomic changes. As one of the important issues for clinicians, it is a hot topic of how to distinguish ALT from benign lipoma in the clinical aspect. Recent studies revealed novel findings to clarify the risk factor for the diagnosis of ALT and molecular targets for the treatment of ALT. Clinical characteristics of superficial-type ALT well reflect the subcutaneous location of the tumor and are slightly different compared to deep-type ALT, such as tumor size. In addition, there has been a recent discovery of novel findings in ALT-related genes, namely, HMG2A (high mobility group protein 2a), YEATS4 (YEATS domain containing 4), and CPM (Carboxypeptidase M). Recent updates on treatment for advanced ALT are well developed including immunotherapy and conducting clinical trials. Finally, this review introduces one of the hot topics of ALT research focused on epigenetic changes: their attention in recent updates on clinical characteristics and the novel discovery of related genes, treatment, and epigenetic modifications in atypical lipomatous tumors.

A Rapid and Cost-Effective Gene Expression Assay for the Diagnosis of Well-Differentiated and Dedifferentiated Liposarcomas

Histologic examination neither reliably distinguishes benign lipomas from atypical lipomatous tumor/well-differentiated liposarcoma, nor dedifferentiated liposarcoma from other pleomorphic sarcomas, entities with different prognoses and management. Molecular confirmation of pathognomonic 12q13-15 amplifications leading to MDM2 overexpression is a diagnostic gold standard. Currently the most commonly used assay for this purpose is fluorescence in situ hybridization (FISH), but this is labor intensive. This study assessed whether newer NanoString-based technology could allow for more rapid and cost-efficient diagnosis of liposarcomas on standard formalin-fixed tissues through gene expression. Leveraging large-scale transcriptome data from The Cancer Genome Atlas, 20 genes were identified, most from the 12q13-15 amplicon, that distinguish dedifferentiated liposarcoma from other sarcomas and can be measured within a single NanoString assay. Using 21 cases of histologically ambiguous low-grade adipocytic tumors with available MDM2 amplification status, a machine learning-based analytical pipeline was built that assigns a given sample as negative or positive for liposarcoma based on quantitative gene expression. The effectiveness of the assay was validated on an independent set of 100 sarcoma samples (including 40 incident prospective cases), where histologic examination was considered insufficient for clinical diagnosis. The NanoString assay had a 93% technical success rate, and an accuracy of 97.8% versus an MDM2 amplification FISH gold standard. NanoString had a considerably faster turnaround time and was cheaper than FISH.

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.

Nuclear expression of MDM2 in hibernoma: a potential diagnostic pitfall

Hibernoma is a rare benign adipocytic tumor composed of a proliferation of brown and white fat cells varying in their proportions. The tumor may also contain fat cells resembling lipoblasts, which makes it difficult to distinguish it from atypical lipomatous tumor/well differentiated liposarcoma (ALT/WDLS). Although nuclear expressions of murine double minute 2 (MDM2) and cyclin-dependent kinase 4 (CDK4) are widely used as immunohistochemical surrogate markers for ALT/WDLS, the utility of these proteins in distinguishing between hibernoma and ALT/WDLS still remains to be elucidated. We evaluated immunohistochemical expressions of MDM2 and CDK4 in 10 hibernomas expressing uncoupling protein-1 (UCP-1), a mitochondrial protein transporter consistently expressed in brown fat cells, and lacking MDM2 gene amplification, which was analyzed by fluorescence in situ hybridization (FISH). In contrast to the data previously obtained, nuclear expression of MDM2 was observed in 100% (10/10 cases) of the hibernomas irrespective of the proportion of brown fat cells, whereas no cases were positive for CDK4. The tumors also showed almost concurrent expression of p53 (in 9/10 cases) and ubiquitin-specific-processing protease 7 (USP7) (in 10/10 cases), which deubiquitinates and stabilizes MDM2, potentially resulting in its nuclear expression without MDM2 gene amplification. MDM2 expression may thus be a diagnostic pitfall for hibernoma particularly in differentiating it from ALT/WDLS.

Well-differentiated liposarcoma primary from thymic stroma: Case report and literature review

Primary liposarcoma of thymic stroma is an exceptionally rare tumor. Histological findings are often definitive for diagnosis, however due to the variability of nuclear atypia and the overlapping with other adipocytic tumors, ancillary techniques are helpful as confirmatory tools. Currently, Fluorescent in situ hybridization for MDM2 is the gold standard for diagnosis of well-differentiated and dedifferentiated liposarcomas, however a panel of immunohistochemical stainings, including MDM2, CDK4 and p16 is available as alternative method, helping to distinguish liposarcoma from its benign counterpart lipoma, especially in borderline cases. We describe the case of a young female diagnosed with a well-differentiated lipomatous tumor primary of thymic stroma with near cut-off result for MDM2-FISHand positive immunohistochemical staining for the panel described above. We discuss the challenges in the diagnosis of this rare entity andpresent an updated literature review.

Dysplastic lipoma: potential diagnostic pitfall of using MDM2 RNA in situ hybridization to distinguish between lipoma and atypical lipomatous tumor

The distinction between lipoma and atypical lipomatous tumor can be challenging in some cases. While detection of MDM2 gene amplification via fluorescence in situ hybridization (FISH) has been well established as a diagnostic tool to distinguish atypical lipomatous tumor and well-differentiated liposarcoma from benign mimics, MDM2 RNA in situ hybridization (RNA-ISH) has recently been proposed as an alternative diagnostic assay. During clinical workup for lipomatous tumors using MDM2 RNA-ISH, we noticed several dysplastic lipomas that were positive for MDM2 RNA-ISH but negative for MDM2 amplification by FISH. In this study, we examined a series of 11 dysplastic lipomas, all confirmed to be negative for MDM2 amplification by FISH. Positive MDM2 RNA-ISH was noted in 10 (91%) dysplastic lipomas. Single-nucleotide polymorphism array on one dysplastic lipoma identified the presence of homozygous deletion of 13q, including the RB1 gene locus with no evidence of MDM2 copy number gain. Our findings on the discordance between MDM2 FISH and MDM2 RNA-ISH highlight the potential utility and pitfalls of using MDM2 RNA-ISH in the distinction of atypical lipomatous tumor and related liposarcomas from dysplastic lipoma.

The Utility of Perilipin in Liposarcomas: PLIN1 Differentiates Round Cell Liposarcoma From Other Round Cell Sarcomas

Liposarcoma is the most common soft tissue sarcoma in adults; however, accurate diagnosis often depends on the use of ancillary molecular testing which can be time consuming and expensive. Myxoid/round cell liposarcoma may be a diagnostic challenge due to the morphologic similarities with other nonadipocytic sarcomas with round cell morphology. Immunohistochemistry may be a helpful adjunct to appropriately triage cases for molecular testing. Perilipin 1 (PLIN1) and perilipin 2 (adipophilin) (PLIN2) are intracellular proteins involved in lipid droplet formation, which we hypothesized may be useful as immunohistochemical markers for liposarcoma. Using archival tumor tissue, we assessed pattern of PLIN1 and PLIN2 expression in 46 adipocytic tumors and 36 nonadipocytic sarcomas. PLIN1 was expressed in 88% of liposarcomas, including 100% of myxoid/round cell liposarcomas, and did not have any expression in nonadipocytic sarcomas. PLIN1 was not expressed in dedifferentiated liposarcoma. Although PLIN2 demonstrates increased sensitivity for liposarcoma, including expression in dedifferentiated liposarcoma, it is not specific for adipocytic differentiation and is expressed in other nonadipocytic sarcomas. Furthermore, PLIN2 is not expressed in lipoma-like well-differentiated liposarcoma, and as such has limited diagnostic utility.

Abdominal Actinomycosis misdiagnosed as liposarcoma

Actinomycosis is an uncommon, endogenous, and chronic infection with varied and nonspecific clinical features such as abdominal, pelvic or cervical masses, ulcerative lesions, abscesses, draining fistula, fibrosis, and constitutional symptoms. The disease ensues when the bacteria disrupt the mucosal barrier, invade, and spread throughout interfascial planes. Currently, the diagnosis of actinomycosis is challenging because of its very low frequency and depending on the clinical presentation it may masquerade malignancies. Therapy consists initially in intravenous penicillin, followed by an oral regimen that may be extended until a year of treatment. A timely diagnosis is crucial to avoid extensive therapeutic attempt as surgery. However, a biopsy or drainage of abscesses and fistula’s tract may be required not only as a diagnostic procedure as part of the therapy. We report the case of a 72-year-old woman with an abdominal mass initially misdiagnosed as a liposarcoma. A second biopsy of a skin lesion of the abdominal wall made the diagnosis of actinomycosis, avoiding a major surgical procedure. The patient was treated with a long-term course of antibiotics with favorable outcome. Liposarcoma was ruled out after the patient’s full recovery with antibiotics and the misdiagnosis was credit to the overconfidence on the immunohistochemical positivity to MDM2.

MDM2 RNA In Situ Hybridization for the Diagnosis of Atypical Lipomatous Tumor: A Study Evaluating DNA, RNA, and Protein Expression

The distinction of atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDL) from its benign counterpart, lipoma, may represent a challenge. MDM2 DNA amplification is used as the gold standard as MDM2 immunohistochemistry lacks specificity and sensitivity. Herein, we investigate the diagnostic utility of MDM2 RNA in situ hybridization (RNA-ISH) and compare the test with MDM2 immunohistochemistry and MDM2 DNA fluorescence in situ hybridization (FISH) in benign and malignant lipomatous neoplasms. We evaluated 109 neoplasms including 27 lipomas, 25 spindle cell lipomas, 32 ALTs/WDLs, and 25 dedifferentiated liposarcomas (DDL). The validation cohort included 14 lipoma-like neoplasms that lacked unequivocal features of ALT/WDL and in which MDM2 immunohistochemistry was either equivocal, negative or falsely positive. Immunohistochemistry, automated RNA-ISH and DNA-FISH for MDM2 were performed. Tumors with diffuse nuclear staining or >50 dots per cell on RNA-ISH were considered positive. All lipomas and lipoma variants were negative for RNA-ISH while all ALTs/WDLs and DDLs were positive. Eighty percent (24/30) and 92% (22/24) of ALTs/WDLs and DDLs were positive for MDM2 immunohistochemistry. Lipomas and its variants were negative for MDM2 amplification; 92% and 100% of ALTs/WDLs and DDLs showed MDM2 DNA amplification. The mean percentage of ALT/WDL tumor cells showing MDM2 RNA-ISH positivity was 73% compared with 24% on MDM2 immunohistochemistry. RNA-ISH correctly classified all 10 ALTs/WDLs and all 4 lipomas in the validation cohort. The performance of MDM2 RNA-ISH and MDM2 DNA-FISH are equivalent. MDM2 RNA-ISH can be of diagnostic value in histologically challenging lipomatous neoplasms. The automated MDM2 RNA-ISH assay should allow for more widespread use of MDM2 testing and for a more sensitive and specific diagnosis of ALT/WDL.

Analysis of Dedifferentiated Liposarcomas Emphasizing the Diagnostic Dilemmas

Introduction: Dedifferentiated liposarcoma (DDLPS) is defined as a progression of well-differentiated liposarcoma (WDLPS) to another nonlipogenic sarcoma. Since a variety of heterologous sarcomas can be encountered in dedifferentiation, clinical dilemmas arise. The present study analyzed the role of clinicopathologic and immunohistochemical (IHC) features in the diagnosis of DDLPS and its differentiation from mimics. Materials and Methods: A retrospective and prospective study was conducted wherein all cases of liposarcoma from 2012 to 2017 were reviewed. DDLPS cases were identified among pleomorphic lesions. Clinical and histopathological details for these cases were retrieved from medical records section and department archives. Histomorphology and immunohistochemistry (MDM2, S100, and Ki-67) were analyzed for these cases. Results: Among 37 cases of liposarcomas reviewed, DDLPS was diagnosed in 12 cases (32.4%). Mean age of the patients was 54.3 years with equal gender distribution (M:F =1:1.2). Two patients had recurrent tumors. Most were retroperitoneal (58.3%) with mean duration of symptoms being 8.7 months. Mean tumor dimension was 17.5 cm. High-grade dedifferentiated component was most common (83.3%) with only one case each (8.3%) of low-grade and homologous dedifferentiation. Undifferentiated pleomorphic sarcoma was the frequent nonlipogenic sarcoma. MDM2 overexpression was detected in 100%, focal S100 positivity seen in 66.6%, and mean Ki-67 labeling index was 24. Conclusion: DDLPS exhibits aggressive clinical behavior. Adequate sampling, correlation to clinical details, demonstration of transition from WDLPS to DDLPS aid in narrowing the differentials. Immunostaining with MDM2 helps in definite categorization and S100 highlights lipoblasts, when they are not easily identifiable. MDM2, CDK4, and p16 IHC panel is recommended in all cases and fluorescence in situ hybridization analysis where IHC is noncontributory.

In-situ recurrence of the primary cardiac dedifferentiated liposarcoma: To resect or not?

Dedifferentiated liposarcoma (DDLPS) is a rare type of neoplasm which can originally rise in cardiac chamber. Owing to the recurrence and distant metastasis, the prognosis of the primary malignant cardiac tumor is extremely poor and remains a challenge for cardiac surgeons. Here, we report a patient with an intracavitary mass which was diagnosed as DDLPS by postoperative pathological examinations, experienced repeated in-situ recurrence of the malignant cardiac tumor.

Primary cardiac dedifferentiated liposarcoma in a middle-aged female: a case report

BACKGROUND

Primary malignant cardiac tumors are extremely rare and can present with the same nonspecific characteristics as benign primary cardiac tumors. We herein describe a middle-aged female with an intracavitary, irregular atrial mass who experienced partial surgical resection. The atrial mass which was recognized as myxoma before surgery was finally diagnosed as dedifferentiated liposarcoma (DDLPS) by postoperative pathological examination.

CASE PRESENTATION

The patient, a 61-year-old female, presented to the emergency room because of progressive chest congestion and shortage of liberties for 6 months and orthopnoea and paroxysmal nocturnal dyspnea for 3 days. The laboratory examinations confirmed no abnormalities. The thoracic computed tomography (CT) scan showed massive hydropericardium, pleural effusion and left atrium occupying lesion. The transesophageal echocardiography (TEE) confirmed an intracavitary and irregular left atrial mass, limiting the mitral valve inflow and pulmonary venous blood reflux. The positron emission tomography/computed tomography (PET/CT) revealed high grade fluorodeoxyglucose uptake only in the intracavitary mass which near the mitral valve. According to operative exploration, the intracavitary mass had invaded the mitral annulus and posterior wall of left ventricle which cannot be resected completely, we did merely partial surgical resection to relieve the patient's symptoms. Postoperative immunohistochemical stain confirmed the diagnosis of DDLPS. The patient was transferred to the oncology department for further therapy. Unfortunately, the patient was detected with brain metastasis 1 month later and died within 5 months after the surgery.

CONCLUSIONS

Primary cardiac DDLPS is an extremely rare histological subtype of undifferentiated pleomorphic sarcomas which present the same nonspecific characteristics as benign primary cardiac tumors. Even though surgical resection combined with chemotherapy or radiotherapy remains the mainstream treatment strategy, the prognosis of cardiac malignancy is poor with high mortality. Novel management strategies need to be further explored.

A Paratesticular Angiolipoma: A Case Report of a Rare Benign Scrotal Mass and Review of Literature

We report a rare case of paratesticular angiolipoma in a young male. The patient is a 21-year-old male who presented with a palpable firm right intrascrotal mass of 21 mm. Ultrasound findings demonstrated that it is a solid mass. Under the diagnosis of an intrascrotal solid mass, a right inguinal radical orchiectomy was performed. Histopathological examination concluded to a paratesticular angiolipoma. Angiolipoma is a rare benign form of paratesticular tumour and its diagnosis is based on histological findings of the surgical specimen with no recurrence risk. This mesenchymal tumour should be distinguished from liposarcoma, which has malignant or aggressive clinical course.

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.

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.

Identification of Coiled-Coil Domain-Containing Protein 180 and Leucine-Rich Repeat-Containing Protein 4 as Potential Immunohistochemical Markers for Liposarcoma Based on Proteomic Analysis Using Formalin-Fixed, Paraffin-Embedded Tissue

Recent technical improvements in both mass spectrometry and protein extraction have made it possible to use formalin-fixed, paraffin-embedded (FFPE) tissues for proteome analysis. In this study, comparable proteome analysis of FFPE tissues revealed multiple candidate marker molecules for differentiating atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDL) from lipoma. A total of 181 unique proteins were identified for ALT/WDL. Of the identified proteins, coiled-coil domain-containing protein 180 (CCDC180) and leucine-rich repeat-containing protein 4 (LRRC4) were studied as candidate markers of ALT/WDL. CCDC180 and LRRC4 immunohistochemistry clearly stained tumor cells of ALT/WDL and dedifferentiated liposarcoma and could differentiate them from lipoma with high accuracy. Cell biological methods were used to further examine the expression of the candidate marker molecules in liposarcoma cells. In liposarcoma cells, knockdown of CCDC180 and LRRC4 inhibited cell proliferation. CCDC180 inhibited cell migration, invasion, and apoptosis resistance in WDL cells. Adipogenic differentiation suppressed the expression of CCDC180 and LRRC4 in WDL cells. These results indicated that LRRC4 and CCDC180 are novel immunohistochemical markers for differentiating ALT/WDLs. Their expression was associated with adipocyte differentiation and contributed to malignant potentials of WDL cells. Proteome analysis using a standard stock of FFPE tissues can reveal novel biomarkers for various diseases, which contributes to the progress of molecular pathology.

Intraoral fibrolipoma: case report and review of literature

Introduction: Lipomas are benign soft tissue tumors, characterized by the presence of mature adipocytes in histopathology. Their development is slow and their etiologies are still controversial. Frequently subcutaneous, this type of lesion is rarely present in the oral cavity. Observation: A 67-year-old man consulted for a nodule on the inner face of his right cheek which had been developing for several years, with severe discomfort during chewing. The typical clinical aspect of this lesion suggested a lipoma. Magnetic resonance imaging (MRI) was performed before surgical excision in order to establish a differential diagnosis with a well-differentiated liposarcoma. Comments: The various imaging examinations, particularly MRI, combined with the analysis of the fat component and the morphology of the non-fat component (septa) enable us to define several categories of lesions likely to have a benign or malignant character. However, some lesions remain difficult to classify, and it is the histopathological examination along with, if necessary, immunohistochemistry (anti-MDM2 and/or anti-CDK4), which allows to confirm or not the malignancy of a lesion. Histological examination suggested a fibrolipoma. Conclusion: Although benign, the size of a fibrolipoma may can lead to significant functional and aesthetic discomfort for the patient. Surgical excision remains the treatment of choice.

Lipomas of the Oral Cavity: Utility of MDM2 and CDK4 in Avoiding Overdiagnosis as Atypical Lipomatous Tumor

Traumatized lipomas with degenerative change may demonstrate histopathologic features that mimic atypical lipomatous tumor (ALT). Previously reported series of ALT involving the oral cavity preceded routine use of MDM2 and CDK4 immunohistochemistry. Our aim is to evaluate MDM2 and CDK4 immunohistochemical expression in adipocytic tumors arising in this site, in conjunction with the histiocytic marker PU.1, to determine whether MDM2 and CDK4 impacts classification. 17 cases originally diagnosed as ALT were retrieved and immunohistochemical studies for MDM2, CDK4 and PU.1 were performed. FISH analysis for MDM2 amplification was performed in select cases. For this study group, the male:female ratio was 9:8 and the median age was 62 (range 41-88). All 17 cases presented as well- or predominantly well-circumscribed proliferations of variably sized, mature adipocytes exhibiting uni- or multi-vacuolation with occasional scalloped nuclei and mild nuclear atypia. Variable amounts of fibrous stroma with focal myxoid change and bland spindle cells were identified in 14/17 cases. Lipoblasts or atypical hyperchromatic stromal cells were not identified in any cases. 14 of 17 cases were negative for MDM2 and CDK4 in tumor cells and 11 of these 14 showed weak nuclear positivity for MDM2 in histiocytes. 3 of 17 cases showed weak, multifocal immunohistochemical expression of MDM2 and CDK4. PU.1 highlighted histiocytes in all 17 cases. FISH analysis for MDM2 amplification was negative in all 3 cases with weak MDM2/CDK4 expression. All cases were reclassified as lipoma with degenerative changes. ALT, in all likelihood, is less common than previously thought in this anatomic location and best diagnosed with ancillary studies. MDM2 expression in histiocytes is best interpreted in conjunction with CDK4 immunohistochemistry and confirmatory FISH for MDM2 amplification.

The Value of MRI in Distinguishing Subtypes of Lipomatous Extremity Tumors Needs Reassessment in the Era of MDM2 and CDK4 Testing

Introduction

Extremity lipomas and well-differentiated liposarcomas (WDLs) are difficult to distinguish on MR imaging. We sought to evaluate the accuracy of MRI interpretation using MDM2 amplification, via fluorescence in-situ hybridization (FISH), as the gold standard for pathologic diagnosis. Furthermore, we aimed to investigate the utility of a diagnostic formula proposed in the literature.

Methods

We retrospectively collected 49 patients with lipomas or WDLs utilizing MDM2 for pathologic diagnosis. Four expert readers interpreted each patient's MRI independently and provided a diagnosis. Additionally, a formula based on imaging characteristics (i.e. tumor depth, diameter, presence of septa, and internal cystic change) was used to predict the pathologic diagnosis. The accuracy and reliability of imaging-based diagnoses were then analyzed in comparison to the MDM2 pathologic diagnoses.

Results

The accuracy of MRI readers was 73.5% (95% CI 61-86%) with substantial interobserver agreement (κ=0.7022). The formula had an accuracy of 71%, which was not significantly different from the readers (p=0.71). The formula and expert observers had similar sensitivity (83% versus 83%) and specificity (64.5% versus 67.7%; p=0.659) for detecting WDLs.

Conclusion

The accuracy of both our readers and the formula suggests that MRI remains unreliable for distinguishing between lipoma and WDLs.

Expression of MDM2 and p16 in angiomyolipoma

Angiomyolipoma (AML) arises primarily from the kidney but may grow into the retroperitoneal space mimicking a primary retroperitoneal tumor. Fine needle aspiration (FNA) and core needle biopsy of AML, particularly the fat-predominant variant, may be difficult to distinguish from retroperitoneal well-differentiated liposarcoma (WDLS) or lipoma. Commonly used immunomarkers, MDM2 and p16, have proven useful in diagnosing WDLS and dedifferentiated liposarcoma (DDLS), while HMB45 and Melan-A are melanocyte-related markers characteristically expressed in AML. In this study, we investigated the utility of MDM2 and p16 along with HMB45 and Melan-A immunohistochemical analysis in distinguishing AML from WDL/DDLS or lipoma. Immunohistochemically, AMLs demonstrated focal MDM2 expression (40% of cases) and focal/diffuse expression of p16 (60%). AMLs marked focally or diffusely with HMB45 (76% of cases) and Melan-A (96%). These latter two immunomarkers were not expressed in any of the WDLS/DDLSs or lipomas tested. WDLS/DDLSs showed focal/diffuse expression of MDM2 (91% of cases) and p16 (97%). While focal expression of MDM2 and p16 was observed in 14% and 67% of lipomas, respectively, no lipoma exhibited diffuse MDM2 positivity. In our hands, MDM2 expression by itself cannot exclude the diagnosis of AML or lipoma, and p16 alone is not helpful in separating AML and conventional lipoma from WDLS/DDLS. However, along with morphology, an immunohistochemical battery including HMB45, Melan-A, MDM2 and p16 are useful in distinguishing AML from WDLS/DDLS or lipoma. For equivocal cases, fluorescence in situ hybridization for MDM2 should be performed.

Perspectives on Low-grade Sarcomas: The Extraordinary Contributions of Sharon W. Weiss, MD

Soft-tissue pathology encompasses a wide spectrum of neoplasms that represent some of the most challenging and problematic tumors in surgical pathology. Owing to the intensive work of dedicated pathologists, this once esoteric field has become increasingly well defined. In this review, Dr Sharon Weiss' monumental contributions to low-grade sarcomas, including low-grade fibromyxoid sarcoma/so-called hyalinizing spindle cell tumor, atypical lipomatous tumor/well-differentiated liposarcoma and dedifferentiated liposarcoma, epithelioid hemangioendothelioma, and dermatofibrosarcoma protuberans with fibrosarcomatous transformation will be discussed.

Recent translational research into targeted therapy for liposarcoma

Liposarcomas (LPS) are among the most common soft tissue sarcomas, originating from adipocytes. Treatment for LPS typically involves surgical resection and radiation therapy, while the use of conventional cytotoxic chemotherapy for unresectable or metastatic LPS remains controversial. This review summarizes the results of recent translational research and trials of novel therapies targeting various genetic and molecular aberrations in different subtypes of LPS. Genetic aberrations such as the 12q13-15 amplicon, genetic amplification of MDM2, CDK4, TOP2A, PTK7, and CHEK1, point mutations in CTNNB1, CDH1, FBXW7, and EPHA1, as the fusion of FUS-DDIT3/EWSR1-DDIT3 are involved in the pathogenesis LPS and represent potential therapeutic candidates. Tyrosine kinase inhibitors targeting MET, AXL, IGF1R, EGFR, VEGFR2, PDGFR-β and Aurora kinase are effective in certain types of LPS. Abnormalities in the PI3K/Akt signaling pathway deregulation of C/EBP-α and its partner PPAR-γ, and the interaction between calreticulin (CRT) and CD47 are also promising therapeutic targets. These promising new approaches may help to supplement existing treatments for LPS.