Application of MDM2 Fluorescence In Situ Hybridization and Immunohistochemistry in Distinguishing Dedifferentiated Liposarcoma From Other High-grade Sarcomas

MDM2 Amplification Status in a Cohort of Well-Characterized Myxofibrosarcoma: A Clinicopathologic Analysis of 22 Tumors

Myxofibrosarcomas (MFS) present as slowly enlarging superficial masses in elderly patients. Even though these tumors fail to exhibit a distinct immunophenotype, diagnosis is straightforward when they present in subcutaneous tissue. Intramuscular MFS, however, are more challenging to diagnose as the differential also includes dedifferentiated liposarcoma with myxoid features. The vast majority of dedifferentiated liposarcomas show MDM2 amplification, whereas limited data exists as to the MDM2 status of MFS. We sought to explore the rate of MDM2 amplification in cases of classic MFS. Our archives were searched for MFS; only subcutaneous well-sampled resections were included. FISH for MDM2 amplification was performed on each tumor. A cohort of myxoid dedifferentiated liposarcoma resections was studied for comparison. Twenty-two MFS arose in patients aged 44 to 85 years. All tumors contained an infiltrative population of atypical cells embedded in a myxoid stroma with curvilinear blood vessels. MDM2 amplification by FISH was identified in 3 (of 22; 14%) tumors. Available follow up on 17 patients (range 1-96 months; median 13 months) revealed 6 patients with local recurrence and 1 with distant metastasis. Of 3 patients with MDM2- amplified MFS, 1 experienced recurrence and died of unrelated causes, while the second was alive without disease 12 months after diagnosis. Even though the rate of MDM2 amplification by FISH in MFS appears to be low, a subset of cases may show this genetic alteration, which pathologists should be aware of to avoid misclassification as myxoid dedifferentiated liposarcomas. Further studies are necessary to determine if amplification status adds prognostic value.

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 Conundrum of Dedifferentiation in a Liposarcoma at a Peculiar Location: A Case Report and Literature Review

Dedifferentiated liposarcoma of the deep soft tissue of the lower extremities is an infrequent finding. Myxoid liposarcoma is considered the most common soft tissue neoplasia arising in this anatomic region. Divergent differentiation usually occurs within well-differentiated liposarcoma and is exceedingly rare in a myxoid liposarcoma. We report a 32-year-old man who developed a dedifferentiated liposarcoma of the thigh on the background of a pre-existing myxoid liposarcoma. The gross examination of the surgical specimen showed a 11/7/2 cm tumour mass with solid tan-grey areas and focal myxoid degeneration. The microscopic examination revealed a malignant lipogenic proliferation, containing round cells with hyperchromatic nuclei and atypical lipoblasts, confined to the basophilic stroma with a myxoid aspect. Abrupt transition towards a hypercellular, non-lipogenic area consisting of highly pleomorphic spindle cells with atypical mitotic figures was also noted. Immunohistochemical staining was performed. Tumour cells in the lipogenic area were intensely positive for S100 and p16, and CD34 staining highlighted an arborizing capillary network. The dedifferentiated tumour areas showed positive MDM2 and CDK4 staining within neoplastic cells, with the Ki 67 proliferation marker expressed in approximately 10% of the cells. Wild-type TP53 protein expression pattern was documented. Thus, the diagnosis of a dedifferentiated liposarcoma was established. This paper aims to provide further knowledge about liposarcomas with divergent differentiation at peculiar locations, emphasizing the importance of histopathologic examination and immunohistochemical analysis for establishing the diagnosis and assessing the therapeutic response and prognosis of this condition.

Primary cardiac undifferentiated pleomorphic sarcoma is associated with TP53 mutation during lack of MDM2 amplification, and targeted sequencing analysis reveals potentially actionable targets

Cardiac undifferentiated pleomorphic sarcoma (UPS) is a rare malignancy. Several studies have revealed frequent MDM2, CDK4, PDFGRA, and KIT amplifications and CDKN2A and CDKN2B deletions. Cases lacking the above copy number alterations may harbor alternative driver mutations; however, little is known about such occurrences. This study was conducted to gain further insights into the molecular features of cardiac UPS using targeted sequencing of 560 cancer-related genes, and fluorescence in situ hybridization and immunohistochemistry of MDM2, CDK4, CDKN2A, TP53, and RB1 in 9 cardiac UPS cases. TP53 mutation or CDKN2A deletion was found in cases lacking MDM2 amplification. Further, p53 overexpression was detected in the case with TP53 mutation, while p16 expression was completely lost in the case with CDKN2A homozygous deletion. p16 overexpression was found in cases with MDM2 and CDK4 amplification but without CDKN2A deletion. Immunohistochemistry of MDM2, CDK4, p53, and p16 is expected to be preliminarily used for gene status analysis. As cardiac UPS and intimal sarcomas are merging into a single spectrum, mutation data for 3 cardiac UPS and 9 intimal sarcomas from the literature, as well as data for 5 cardiac UPS in our study were evaluated, and known recurrently mutated cancer driver genes, including PDGFRB, TP53, ALK, PTCH1, RET, ERBB4, JAK3, GATA1, PIK3CG, and RARA, were identified. Several new potentially actionable mutations, including those in RARA, ALK, PTCH1, RET, ROS1, ABL1, and MET, were also found. These findings improve the molecular understanding of this rare malignancy and are expected to provide a basis for developing precision therapeutics for cardiac UPS and intimal sarcomas.

Fluorine-18 Labeling of the MDM2 Inhibitor RG7388 for PET Imaging: Chemistry and Preliminary Evaluation

RG7388 (Idasanutlin) is a potent inhibitor of oncoprotein murine double minute 2 (MDM2). Herein we investigated the feasibility of developing ¹⁸F-labeled RG7388 as a radiotracer for imaging MDM2 expression in tumors with positron emission tomography (PET). Two fluorinated analogues of RG7388, 6 and 7, were synthesized by attaching a fluoronicotinyl moiety to RG7388 via a polyethylene glycol (PEG₃) or a propyl linker. The inhibitory potency (IC₅₀) of 6 and 7 against MDM2 was determined by a fluorescence polarization (FP)-based assay. Next, compound 6 was labeled with ¹⁸F using a trimethylammonium triflate precursor to obtain [¹⁸F]FN-PEG₃-RG7388 ([¹⁸F]6), and its properties were evaluated in MDM2 expressing wild-type p53 tumor cell lines (SJSA-1 and HepG2) in vitro and in tumor xenografts in vivo. The FP assays revealed an IC₅₀ against MDM2 of 119 nM and 160 nM for 6 and 7, respectively. ¹⁸F-labeling of 6 was achieved in 50.3 ± 7.5% radiochemical yield. [¹⁸F]6 exhibited a high uptake (∼70% of input dose) and specificity in SJSA-1 and HepG2 cell lines. Saturation binding assays revealed a binding affinity (K_d) of 128 nM for [¹⁸F]6 on SJSA-1 cells. In mice, [¹⁸F]6 showed fast clearance from blood with a maximum tumor uptake of 3.80 ± 0.85% injected dose per gram (ID/g) in HepG2 xenografts at 30 min postinjection (p.i.) and 1.32 ± 0.32% ID/g in SJSA-1 xenografts at 1 h p.i. Specificity of [¹⁸F]6 uptake in tumors was demonstrated by pretreatment of mice with SJSA-xenografts with a blocking dose of RG7388 (35 mg/kg body weight, i.p.). In vivo stability studies in mice using HPLC showed ∼60% and ∼30% intact [¹⁸F]6 remaining in plasma at 30 min and 1 h p.i., respectively, with the remaining activity attributed to polar peaks. Our results suggest that RG7388 is a promising molecular scaffold for ¹⁸F-labeled probe development for MDM2. Additional labeling strategies and functionalizing locations on RG7388 are under development to improve binding affinity and in vivo stability of the ¹⁸F-labeled compound to make it more amenable for PET imaging of MDM2 in vivo.

The many faces of solitary fibrous tumor; diversity of histological features, differential diagnosis and role of molecular studies and surrogate markers in avoiding misdiagnosis and predicting the behavior

Background

Solitary Fibrous Tumor (SFT) is a distinct soft tissue neoplasm associated with NAB2-STAT6 gene fusion. It can involve a number of anatomic sites and exhibits a wide spectrum of histological features.

Main body

Apart from diversity in morphological features seen even in conventional SFT, two histologic variants (fat-forming and giant cell-rich) are also recognized. In addition, a malignant form and dedifferentiation are well recognized. Owing to diverse histological features and involvement of diverse anatomic locations, SFT can mimic other soft tissue neoplasms of different lineages including schwannoma, spindle cell lipoma, dermatofibrosarcoma protuberans, liposarcoma, gastrointestinal stromal tumor (GIST), malignant peripheral nerve sheath tumor (MPNST), and synovial sarcoma. SFT is classified as an intermediate (rarely metastasizing) tumor according to World Health Organization Classification of Tumors of Soft tissue and Bone, 5th edition. The management and prognosis of SFT differs from its malignant mimics and correct diagnosis is therefore important. Although SFT expresses a distinct immunohistochemical (IHC) profile, the classic histomorphological and IHC profile is not seen in all cases and diagnosis can be challenging. NAB2-STAT6 gene fusion has recently emerged as a sensitive and specific molecular marker and its IHC surrogate marker signal transducer and activator of transcription 6 (STAT6) has also shown significant sensitivity and specificity. However, few recent studies have reported STAT6 expression in other soft tissue neoplasms.

Conclusion

This review will focus on describing the diversity of histological features of SFT, differential diagnoses and discussing the features helpful in distinguishing SFT from its histological mimics.

A single institutional experience treating adipocytic tumors: incidence, disease-related outcomes, and the clinical significance of MDM2 analysis

Adipocytic tumors exist either as a benign or malignant form. The benign variant, lipoma, is composed of normal fat tissue. Lipomas typically develop from superficial fat cells beneath the skin or mucous membranes. Liposarcoma, the malignant counterpart, often develops in deeper tissues and is the most commonly diagnosed Soft Tissue Sarcoma (STS), comprising at least 20% of adult STS. However, malignant tumors of fatty origin exist as a spectrum of diagnoses, each carrying a unique risk of recurrence, metastasis, and longterm survival. The World Health Organization classifies liposarcomas into five categories: i) Atypical Lipomatous Tumors/Well Differentiated (ALT/WD); Ii) Dedifferentiated (ALT/DD); Iii) Myxoid; Iv) Round cell; and v) Pleomorphic. Lipomatous tumors often exhibit different immunohistochemical patterns. Benign lipomas are distinguished by the absence of Murine Double-Minute 2 (MDM2) amplification. Similarly, ALT/WD, classically defined as a low-grade and locally aggressive tumor, demonstrates consistent patterns of MDM2 amplification. Some studies suggest 10% of ALT/WD progress to the highgrade DD form, with others report a dedifferentiation rate of as high as 20% for primary ALT/WD based on location. The ALT/DD subtype is aggressive and has a high capacity to metastasize. While the mechanism of pathogenesis of ALT/DD metastasis is unknown, previous studies suggest that increased MDM2 amplification may play a role. This study sought to evaluate a single institutional experience treating the entire spectrum of lipomatous tumors and describe utilization patterns of MDM2 testing. The group hypothesized: i) Atypical Lipomatous Tumors (ALT), which include ALT/DD and ALT/WD, would exhibit a higher rate of local recurrence than lipomas with no significantly increased incidence of metastases; and ii) at least 50% of our MDM2 testing of ALT would prove positive for the MDM2 overamplification. This study retrospectively reviewed 105 cases (66 lipomas, 27 ALTs, 12 liposarcomas) of patients who underwent lipomatous tumor excision at our institution from 2013 to 2017. Twenty-five tumors (6 lipomas, 18 ALT, 1 liposarcoma) were tested for MDM2 amplification. Three of the tested tumors recurred (2 ALT, 1 liposarcoma), and each exhibited MDM2 overamplification. Five tumors (5 liposarcoma) developed late metastases. These data suggest that although ALT is associated with a higher rate of local recurrence, metastases are quite rare. Additionally, the data demonstrate a high rate of positive MDM2 testing (76%) based on clinical and imaging characteristics of the tumors.

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.

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.

Amplification of MDM2 and Loss of p16 Expression: Do They Have a Role in Malignant Transformation of Ovarian Brenner Tumor?

OBJECTIVES

To review the significance of MDM2 and cyclin D1 expression and loss of p16 expression in malignant and borderline Brenner tumors (BTs) of the ovary.

METHODS

We describe 2 new cases of ovarian BT, 1 malignant and 1 borderline. We studied MDM2, p16, and cyclin D1 expression by immunohistochemistry in the benign, borderline, and malignant components of these 2 cases and in 5 additional cases of benign BT. We also reviewed and summarized the literature on the clinical, immunohistochemical and molecular characteristics of borderline and malignant BTs (BdBTs and MBTs).

RESULTS

Nuclear expression of MDM2 was seen only in the MBT. Loss of p16 expression was seen in both BdBT and MBT. Cyclin D1 expression was in proportion to the degree of malignancy. Amplification of MDM2, loss of CDKN2A (p16-encoding gene), and amplification of CCND1 (cyclin D1-encoding gene) were confirmed by commercial next-generation sequencing in the case of MBT.

CONCLUSIONS

We are the first to report immunohistochemical expression of MDM2 in an MBT. Amplification of MDM2 and loss of p16 expression may have a role in malignant transformation of BT.

Mesenchymal neoplasms: Is it time for cytology? New perspectives for the pre-operative diagnosis of soft tissue tumors in the molecular era

Soft tissue tumors comprise a great variety of common and rare entities with overlapping features. Their diagnosis is based on the evaluation of several histological parameters which are difficult to assess on small incisional biopsies. Useful diagnostic markers in the field of soft tissue tumors include: 1) molecular biomarkers detecting pathogenetically relevant, distinctive alterations; 2) immunohistochemical surrogate biomarkers of pathogenetically relevant, distinctive molecular alterations; 3) highly specific immunohistochemical biomarkers indicating tumor differentiation. Their introduction in clinical practice has revolutionized the pre-operative diagnosis of soft tissue tumors. Cytology has long been considered inadequate as a first-line approach in this setting. However, since the implementation of new immunohistochemical and molecular tests with high diagnostic specificity, fine needle aspiration cytology (FNAC) is starting to gain acceptance for the pre-operative assessment of soft tissue tumors. FNAC represents a versatile, poorly expensive and well-tolerated diagnostic strategy with relevant advantages over histological biopsies. Moreover, evidences suggest that, in expert hands, FNAC can also aim at a definite diagnosis, especially if a cell block is prepared, allowing the application of multiple ancillary techniques.

Extraskeletal Osteosarcoma: Outcomes and the Role of Chemotherapy

OBJECTIVES

Extraskeletal osteosarcoma (EO) is a malignant neoplasm that produces osteoid, bone, and chondroid material without direct attachment to bone or periosteum. Surgical resection is the mainstay of treatment; the role of chemotherapy is not well defined. Therefore, we evaluated the impact of chemotherapy in the survival of patients with EO.

METHODS

All EO patients seen at Mayo Clinic between 1990 and 2014 were assessed. Forty-three patients were included after all archived pathology slides were reviewed to confirm the diagnosis of EO.

RESULTS

Of 43 patients, 37 patients had localized disease and 6 patients had metastatic disease at diagnosis. Chemotherapy was used in 73% and 75% of patients, respectively. Chemotherapy was predominantly anthracycline based, and included platinum in 22 patients (84%).Median overall survival (OS) and progression-free survival (PFS) were 50 months (95% confidence interval, 25-99), and 21 months (95% confidence interval, 13-not reached), respectively. There was a trend towards longer OS and PFS in patients who received chemotherapy. Those who received platinum-based therapy had remarkably prolonged OS (median, 182 vs. 18 mo; 5-year, 61% vs. 0%; P=0.01) and PFS (median, not reached vs. 10 mo; 5-year, 56% vs. 0%; P=0.005). Baseline characteristics were similar in the platinum and nonplatinum group.In patients who received chemotherapy, relapse/recurrence rate was lower in the platinum-based group (41%) as opposed to the nonplatinum-based group (100%; P=0.02). In the neoadjuvant setting, the overall response rate of platinum-containing regimens was 27%.

CONCLUSIONS

Our results suggest a clinical benefit when platinum-based chemotherapy is incorporated in the management of patients with EO. We plan to validate this further with an expanded multicenter analysis.

Primary hepatic gastrointestinal stromal tumor with right adrenal gland invasion: A case report and systematic literature review

INTRODUCTION

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors that mainly occur in the gastrointestinal tract. The GISTs that are sporadically reported in extra-gastrointestinal regions are named as extra-gastrointestinal stromal tumors (EGISTs). However, the primary EGISTs that originate from the liver are rare.

PATIENT CONCERNS

A 64-year-old female presenting with right upper abdominal pain and thirsty for more than 20 days.

DIAGNOSIS

A diagnosis of a 15 × 14 × 7 cm liver mass located in the posterior right lobe of liver and spread to the right adrenal gland was confirmed. Pathological results showed that the tumor was mainly composed of epithelial cells and tested positive for CD117 and SDHB (succinate dehydrogenase complex iron sulfur subunit B). The gene mutational analyses for c-Kit and platelet-derived growth factor receptor alpha exons revealed negative results. Fluorescence in situ hybridization of murine double minute 2 produced negative fluorescence results which distinguished it from dedifferentiated liposarcomas. The postoperative gastroduodenal and colorectal endoscopy did not find any neoplastic lesions. To this end, the diagnosis of primary hepatic EGIST of wild type nature was confirmed.

INTERVENTIONS

The patient received right hepatectomy and adrenalectomy, no postoperative chemotherapy was administered.

OUTCOMES

The patient died 11 months after surgery due to tumor metastasis.

CONCLUSION

Primary hepatic EGIST is a rare and complicated disease of liver, a multidisciplinary team is necessary in diagnosis and treatment of primary hepatic EGIST.

Observing DNA in live cells

The structural organization and dynamics of DNA are known to be of paramount importance in countless cellular processes, but capturing these events poses a unique challenge. Fluorescence microscopy is well suited for these live-cell investigations, but requires attaching fluorescent labels to the species under investigation. Over the past several decades, a suite of techniques have been developed for labeling and imaging DNA, each with various advantages and drawbacks. Here, we provide an overview of the labeling and imaging tools currently available for visualizing DNA in live cells, and discuss their suitability for various applications.

Extrapleural solitary fibrous tumor: A distinct entity from pleural solitary fibrous tumor. An update on clinical, molecular and diagnostic features

Solitary fibrous tumor (SFT) is a mesenchymal neoplasm that was originally described to be localized in the pleura, but thereafter, this has been reported in several anatomic sites. Although the etiology of the neoplasm remains largely unknown, the pathogenesis seems to be related to an NAB2-STAT6 fusion gene due to paracentric inversion on chromosome 12q13. The diagnosis of extrapleural SFT is challenging, owing to its rarity, and requires an integrated approach that includes specific clinical, histological, immunohistochemical, and even molecular findings. Histologically, extrapleural SFT shares morphological features same as those of the pleural SFT because it is characterized by a patternless distribution of both oval- and spindle-shaped cells in a variable collagen stroma. In addition, morphological variants of mixoid, fat-forming, and giant cell-rich tumors are described. A correct diagnosis is mandatory for a proper therapy and management of the patients with extrapleural SFT, as extrapleural SFT is usually more aggressive than pleural form, particularly cases occurring in the mediastinum, retroperitoneum, pelvis, and meninges. Although SFT is usually considered as a clinically indolent neoplasm, the prognosis is substantially unpredictable and only partially related to morphological features. In this context, cellularity, neoplastic borders, cellular atypias, and mitotic activity can show a wide range of variability. We review extrapleural SFT by discussing diagnostic clues, differential diagnosis, recent molecular findings, and prognostic factors.

Pleomorphic fibroma of the skin with MDM2 immunoreactivity: A potential diagnostic pitfall

Pleomorphic fibroma is a rare benign cutaneous neoplasm characterized by spindle-shaped cells and multinucleated giant cells scattered throughout collagenous stroma. These morphologic features can lead to diagnostic confusion, including atypical lipomatous tumor as one consideration. In contrast to atypical lipomatous tumor, previous studies have found pleomorphic fibroma to be negative for MDM2 immunohistochemical staining and MDM2 gene amplification. Here, we present a case of pleomorphic fibroma of skin with nuclear MDM2 immunoreactivity in the absence of MDM2 gene amplification, underscoring the superiority of fluorescence in situ hybridization as a diagnostic test in this differential diagnosis. The RB1 locus is also explored for differential diagnosis with pleomorphic/spindle cell lipoma and related entities.

Application of Fluorescence In Situ Hybridization (FISH) Technique for the Detection of Genetic Aberration in Medical Science

Fluorescence in situ hybridization (FISH) is a macromolecule recognition technique, which is considered as a new advent in the field of cytology. Initially, it was developed as a physical mapping tool to delineate genes within chromosomes. The accuracy and versatility of FISH were subsequently capitalized upon in biological and medical research. This visually appealing technique provides an intermediate degree of resolution between DNA analysis and chromosomal investigations. FISH consists of a hybridizing DNA probe, which can be labeled directly or indirectly. In the case of direct labeling, fluorescent nucleotides are used, while indirect labeling is incorporated with reporter molecules that are subsequently detected by fluorescent antibodies or other affinity molecules. FISH is applied to detect genetic abnormalities that include different characteristic gene fusions or the presence of an abnormal number of chromosomes in a cell or loss of a chromosomal region or a whole chromosome. It is also applied in different research applications, such as gene mapping or the identification of novel oncogenes. This article reviews the concept of FISH, its application, and its advantages in medical science. 

Dedifferentiated Liposarcoma of the Retroperitoneum With Heterologous Osteosarcomatous Differentiation and a Striking Aneurysmal Bone Cyst–Like Morphology

A 69-year-old woman with a 10-year medical history of recurrent retroperitoneal dedifferentiated liposarcoma presented with a 3-cm large hemorrhagic and multicystic left-sided retroperitoneal mass. Histopathological examination of the resected specimen showed a heterogeneous, high-grade mesenchymal nonlipogenic tumor with areas of osteoblastic/osteosarcomatous differentiation and aneurysmal bone cyst–like features. Based on the clinical presentation, the morphology, and the supportive immunohistochemical and molecular findings (MDM2 overexpression and amplification of the MDM2 gene, respectively), a diagnosis of a dedifferentiated liposarcoma with heterologous osteosarcomatous differentiation and an aneurysmal bone cyst–like morphology was made. To the best of our knowledge, this is the first description of aneurysmal bone cyst–like morphology in dedifferentiated liposarcoma, further expanding the broad morphological spectrum of dedifferentiated liposarcoma.