Detection of GNAS mutations in intramuscular / cellular myxomas as diagnostic tool in the classification of myxoid soft tissue tumors

Intramuscular myxoma: unusual observation of spontaneous tumor size shrinkage

Soft tissue tumors, whether benign or malignant, may grow over time or remain stable, but they usually do not spontaneously decrease in size. However, there are exceptions, such as inflammatory conditions, desmoid tumors, or benign cysts. Intramuscular myxomas are benign soft tissue tumors that typically present as a solitary, slow-growing, painless mass. They are generally treated by surgical resection, after which recurrence is rare. Here, we present a brief series of three unusual cases of intramuscular myxomas that spontaneously decreased in size. They were located in the cervical region, the right lower extremity, and the paravertebral lumbar region. Imaging findings and percutaneous biopsies confirmed the diagnosis in all cases. Follow-up imaging showed a spontaneous reduction in lesion volume over time, far exceeding the amount of tissue sample removed during biopsy. This unusual observation of spontaneous shrinkage may call into question the subsequent therapeutic approach to these lesions.

The role of molecular pathology in soft tissue tumor diagnosis: what the radiologist needs to know

For both general radiologists and those specializing in soft tissue sarcoma imaging, understanding the importance and basic concepts of molecular pathology is becoming increasingly relevant to current clinical practice. As molecular research identifies the most fundamental causes and markers of disease, diagnostic testing is increasingly focused on the cell nucleus and its genetic material. Identifying molecular abnormalities, such as mutations, deletions, and amplifications, has advanced our ability to diagnose genetic diseases, including a variety of cancers. Over the past two decades, molecular pathology has rapidly evolved, enhancing our understanding of sarcoma pathogenesis, diagnosis, and classification. This progress forms the foundation of the 2020 WHO classification of soft tissue and bone tumors. This article will highlight cases where molecular diagnostics are crucial for the definitive classification and diagnosis of select soft tissue tumors, with MRI correlation and key teaching points.

Mazabraud's syndrome in female patients: Two case reports

BACKGROUND

Mazabraud's syndrome (MS) is a rare and slowly progressive benign disease characterized by the concurrent presence of fibrous dysplasia of bone and intramuscular myxoma, and is thought to be associated with mutations of the GNAS gene. To date, only about 100 cases of MS have been reported in the literature, but its standard treatment strategy remains unclear.

CASE SUMMARY

We report two cases of MS in young women who underwent different treatments based on their symptoms and disease manifestations. The first patient, aged 37, received internal fixation and intravenous bisphosphonate for a pathological fracture of the right femoral neck, excision of a right vastus medialis myxoma was subsequently performed for pain control, and asymptomatic psoas myxomas were monitored without surgery. Genetic testing confirmed a GNAS gene mutation in this patient. The second patient, aged 24, underwent right vastus intermedius muscle myxoma resection, and conservative treatment for fibrous dysplasia of the ilium. These patients were followed-up for 17 months and 3 years, respectively, and are now in a stable condition.

CONCLUSION

Various treatments have been selected for MS patients who suffer different symptoms. The main treatment for myxomas is surgical resection, while fibrous dysplasia is selectively treated if the patient experiences pathological fracture or severe pain. However, given the documented instances of malignant transformation of fibrous dysplasia in individuals with MS, close follow-up is necessary.

The Role of Methylation Analysis in Distinguishing Cellular Myxoma from Low-Grade Myxofibrosarcoma

Cellular myxoma is a benign soft tissue tumor frequently associated with GNAS mutation that may morphologically resemble low-grade myxofibrosarcoma. This study aimed to identify the undescribed methylation profile of cellular myxoma and compare it to myxofibrosarcoma. We performed molecular analysis on twenty cellular myxomas and nine myxofibrosarcomas and analyzed the results using the methylation-based DKFZ sarcoma classifier. A total of 90% of the cellular myxomas had GNAS mutations (four loci had not been previously described). Copy number variations were found in all myxofibrosarcomas but in none of the cellular myxomas. In the classifier, none of the cellular myxomas reached the 0.9 threshold. Unsupervised t-SNE analysis demonstrated that cellular myxomas form their own clusters, distinct from myxofibrosarcomas. Our study shows the diagnostic potential and the limitations of molecular analysis in cases where morphology and immunohistochemistry are not sufficient to distinguish cellular myxoma from myxofibrosarcoma, particularly regarding GNAS wild-type tumors. The DKFZ sarcoma classifier only provided a valid prediction for one myxofibrosarcoma case; this limitation could be improved by training the tool with a more considerable number of cases. Additionally, the classifier should be introduced to a broader spectrum of mesenchymal neoplasms, including benign tumors like cellular myxoma, whose distinct methylation pattern we demonstrated.

Right adductor compartment intramuscular myxoma: A rare case report

INTRODUCTION

Extracardiac intramuscular myxomas are exceedingly rare benign tumors, necessitating well-planned management for optimal outcomes.

CASE PRESENTATION

We report the case of a 63-year-old male with no prior medical history, presenting with a progressively enlarging mass within the adductor compartment of the right thigh. Physical examination revealed a mobile and painless mass measuring 70 mm by 50 mm at the level of the adductor compartment of the right thigh, devoid of signs of inflammation or skin lesions. The patient showed no cachexia, asthenia, or weight loss. Imaging exams confirmed the characteristic features of intramuscular myxoma, leading to the decision for complete surgical excision. Subsequent histological analysis confirmed the diagnosis, and the patient experienced no postoperative complications, showing positive long-term follow-up results.

CLINICAL DISCUSSION

In the presence of an intramuscular mass, thorough questioning and meticulous clinical examination enable us to propose a diagnosis of intramuscular myxoma. MRI is the preferred imaging modality, supporting diagnostic reasoning. However, histopathological analysis remains essential to confirm the mass's nature and rule out potential malignant differential diagnoses. Complete surgical resection is considered the gold standard, ensuring favorable results with a low risk of recurrence.

CONCLUSION

Extracardiac intramuscular myxomas are exceptionally rare; MRI and histopathological analysis combined help rule out potential malignant differential diagnoses. Total surgical excision yielded good results with a low risk of recurrence.

Genetic characterization of intramuscular myxomas

Introduction: Intramuscular myxomas are benign tumors that are challenging to diagnose, especially on core needle biopsies. Acquired chromosomal aberrations and pathogenic variants in codon 201 or codon 227 in GNAS complex locus gene (GNAS) have been reported in these tumors. Here we present our genetic findings in a series of 22 intramuscular myxomas. Materials and methods: The tumors were investigated for the presence of acquired chromosomal aberrations using G-banding and karyotyping. Pathogenic variants in codon 201 or codon 227 of GNAS were assessed using direct cycle Sanger sequencing and Ion AmpliSeq Cancer Hotspot Panel v2 methodologies. Results: Eleven tumors carried chromosomal abnormalities. Six tumors had numerical, four had structural, and one had both numerical and structural chromosomal aberrations. Gains of chromosomes 7 and 8 were the most common abnormalities being found in five and four tumors respectively. Pathogenic variants in GNAS were detected in 19 myxomas (86%) with both methodologies. The detected pathogenic variants were p.R201H in nine cases (seven with abnormal and two with normal karyotypes), p.R201C in five cases, all with normal karyotypes, p.R201S in three cases (two with abnormal and one with normal karyotype), p.R201G in one case with a normal karyotype, and p.Q227E in one case with a normal karyotype. Conclusion: Firstly, our data indicate a possible association between chromosomal abnormalities and GNAS pathogenic variants in intramuscular myxomas. Secondly, the presence of the rare pathogenic variants R201S, p.R201G and p.Q227E in 26% (5 out of 19) of myxomas with GNAS pathogenic variants shows that methodologies designed to detect only the common "hotspot" of p.R201C and p.R201H will give false negative results. Finally, a comparison between Ion AmpliSeq Cancer Hotspot Panel v2 and direct cycle Sanger sequencing showed that direct cycle Sanger sequencing provides a quick, reliable, and relatively cheap method to detect GNAS pathogenic variants, matching even the most cutting-edge sequencing methods.

Sarcoma care in the era of precision medicine

Sarcoma subtype classification is currently mainly based upon histopathological morphology. Molecular analyses have emerged as an efficient addition to the diagnostic workup and sarcoma care. Knowledge about the sarcoma genome increases, and genetic events that can either support a histopathological diagnosis or suggest a differential diagnosis are identified, as well as novel therapeutic targets. In this review, we present diagnostic, therapeutic, and prognostic molecular markers that are, or might soon be, used clinically. For sarcoma diagnostics, there are specific fusions highly supportive or pathognomonic for a diagnostic entity-for instance, SYT::SSX in synovial sarcoma. Complex karyotypes also give diagnostic information-for example, supporting dedifferentiation rather than low-grade central osteosarcoma or well-differentiated liposarcoma when detected in combination with MDM2/CDK4 amplification. Molecular treatment predictive sarcoma markers are available for gastrointestinal stromal tumor (GIST) and locally aggressive benign mesenchymal tumors. The molecular prognostic markers for sarcomas in clinical practice are few. For solitary fibrous tumor, the type of NAB2::STAT6 fusion is associated with the outcome, and the KIT/PDGFRA pathogenic variant in GISTs can give prognostic information. With the exploding availability of sequencing technologies, it becomes increasingly important to understand the strengths and limitations of those methods and their context in sarcoma diagnostics. It is reasonable to believe that most sarcoma treatment centers will increase the use of massive-parallel sequencing soon. We conclude that the context in which the genetic findings are interpreted is of importance, and the interpretation of genomic findings requires considering tumor histomorphology.

Intramuscular myxoma of the left thigh: A case report

Introduction and clinical importance

Intramuscular myxoma (IM) is a rare benign soft tissue tumor that involves the musculoskeletal system with a reported incidence of 0.1–0.13 per 100,000. The mean age of diagnosis is 40–70 years of age, with female predilection. The most common site of involvement is the thigh, however, it may present in other areas such as the upper arm, calf, and buttock.

Case presentation

A case of a 45-year-old female without a significant past medical or surgical history who presented with 3-year history of a slow-growing, painless mass in her left upper thigh. MRI scan was performed which showed intramuscular soft tissue mass lesion 9 × 6 × 4.5 cm implicating the left distal vastus medialis muscle. A fine needle aspiration was inconclusive so a core needle biopsy was performed which was suggestive of intramuscular myxoma. A complete surgical excision of the mass was done and the postoperative period was uneventful and patient was discharged home. The final histopathological examination confirmed the diagnosis of intramuscular myxoma.

Discussion

Intramuscular myxoma is a rare benign soft tissue neoplasm. 50 % of cases commonly occur in the thigh. IM has an unknown etiology, however, the literature has showed common gene mutations such as the GNAS gene mutations (Guanine nucleotide binding protein, alpha stimulating). Imaging modalities such as ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI) are useful in diagnosis of soft tissue mass but not specific to intramuscular myxoma. Histopathological examination is the gold standard for diagnosis. The treatment of choice is surgical excision with clear margins to prevent recurrence, which is extremely rare.

Conclusion

Intramuscular myxomas, although benign and rare, should be in the differential diagnosis of soft tissue lesions due to the similarity they share with malignant tumors such as sarcomas. Histopathological examination is the gold standard for diagnosing a soft tissue lesion and surgical excision is the treatment of choice.

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Soft tissue masses are common but intramuscular myxoma is a rare differential diagnosis

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Clinical examination and imaging modalities are inconclusive in formulating the diagnosis of intramuscular myxoma

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Histopathological examination is the gold standard for diagnosing cases of intramuscular myxoma

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Surgical excision with a gross negative margin is the treatment of choice

Artificial intelligence significantly improves the diagnostic accuracy of deep myxoid soft tissue lesions in histology

Deep myxoid soft tissue lesions have posed a diagnostic challenge for pathologists due to significant histological overlap and regional heterogeneity, especially when dealing with small biopsies which have profoundly low accuracy. However, accurate diagnosis is important owing to difference in biological behaviors and response to adjuvant therapy, that will guide the extent of surgery and the need for neo-adjuvant therapy. Herein, we trained two convolutional neural network models based on a total of 149,130 images representing diagnoses of extra skeletal myxoid chondrosarcoma, intramuscular myxoma, low-grade fibromyxoid sarcoma, myxofibrosarcoma and myxoid liposarcoma. Both AI models outperformed all the pathologists, with a significant improvement of accuracy up to 97% compared to average pathologists of 69.7% (p < 0.00001), corresponding to 90% reduction in error rate. The area under curve of the best AI model was on average 0.9976. It could assist pathologists in clinical practice for accurate diagnosis of deep soft tissue myxoid lesions, and guide clinicians for precise and optimal treatment for patients.

Extent of Extraskeletal Manifestations of Fibrous Dysplasia/McCune-Albright Syndrome in Patients with Mazabraud's Syndrome

Mazabraud's syndrome (MZB) is a rare condition in which fibrous dysplasia of bone/the McCune-Albright syndrome (FD/MAS) co-exists with intramuscular myxomas. Both FD and the myxomas harbor the GNAS-mutation. Recent studies have shown that extraskeletal, GNAS-related features are associated with a more severe phenotype of FD/MAS. However, patients with MZB are often only seen by orthopedic surgeons. We therefore evaluated MZB patients seen in tertiary referral centers from the Netherlands (LUMC), USA (National Institutes of Health) and France (INSERM UMR 1033 (Lyos), Hôpital Edouard Herriot). All FD/MAS patients known in these centers with an additional diagnosis of a myxoma were included. Demographic information and data on disease extent and extraskeletal manifestations of FD/MAS such as precocious puberty (PP) or café-au-lait patches (CAL) were retrieved from patient's medical records. Thirty MZB patients were included: 20 women (67%) and 10 men (33%). Patients received a diagnosis of MZB (median 42 years, range 16-19) significantly later than the diagnosis of FD/MAS (median 30 years, range 0-60), p < 0.01. Twenty-six patients were diagnosed with polyostotic disease (87%). In 97% the myxoma was located near the skeletal FD lesion. The combination of MZB and MAS was made in 13 patients in whom PP (n = 7), CAL (n = 7), GH-excess (n = 3) and hyperthyroidism (n = 3) were present. Other extraskeletal features were (multinodular) goiter (n = 2) and thyroid cysts (n = 1). Furthermore, in this cohort of patients with MZB several (pre-)malignant tumors were observed; ductal carcinoma in situ of the breast in 3 patients (10%), breast cancer in 1 patient (3.3%), intra pancreatic mucinous neoplasms in 3 patients (10%) and liver adenomas in 2 patients (6.6%). A total of 47% of patients with MZB had an additional extraskeletal feature such as an endocrinopathy. In MZB, 87% of patients suffer from polyostotic FD, 43% of patients have extraskeletal GNAS-features such as an hyperfunctioning endocrinopathy and 30% (pre-)malignant tumors. We therefore advocate that MZB patients should undergo a complete screening and long-term follow-up for extent of bone disease, but also extraskeletal GNAS features of FD/MAS.

OUP accepted manuscript

Intramuscular myxoma (IM) is a rare benign tumour. It may occur at any age but most commonly occurs among older women. The preoperative diagnosis of IM is complicated. The diagnosis can only be definitively established by histopathological examination. The treatment of choice is radical surgical excision. We report a case of a 41-year-old woman with an IM of the biceps brachii muscle.

Update on MR Imaging of Soft Tissue Tumors of Head and Neck

This article reviews soft tissue tumors of the head and neck following the 2020 revision of WHO Classification of Soft Tissue and Bone Tumours. Common soft tissue tumors in the head and neck and tumors are discussed, along with newly added entities to the classification system. Salient clinical and imaging features that may allow for improved diagnostic accuracy or to narrow the imaging differential diagnosis are covered. Advanced imaging techniques are discussed, with a focus on diffusion-weighted and dynamic contrast imaging and their potential to help characterize soft tissue tumors and aid in distinguishing malignant from benign tumors.

Gαs-Protein Kinase A (PKA) Pathway Signalopathies: The Emerging Genetic Landscape and Therapeutic Potential of Human Diseases Driven by Aberrant Gαs-PKA Signaling

Many of the fundamental concepts of signal transduction and kinase activity are attributed to the discovery and crystallization of cAMP-dependent protein kinase, or protein kinase A. PKA is one of the best-studied kinases in human biology, with emphasis in biochemistry and biophysics, all the way to metabolism, hormone action, and gene expression regulation. It is surprising, however, that our understanding of PKA's role in disease is largely underappreciated. Although genetic mutations in the PKA holoenzyme are known to cause diseases such as Carney complex, Cushing syndrome, and acrodysostosis, the story largely stops there. With the recent explosion of genomic medicine, we can finally appreciate the broader role of the Gαs-PKA pathway in disease, with contributions from aberrant functioning G proteins and G protein-coupled receptors, as well as multiple alterations in other pathway components and negative regulators. Together, these represent a broad family of diseases we term the Gαs-PKA pathway signalopathies. The Gαs-PKA pathway signalopathies encompass diseases caused by germline, postzygotic, and somatic mutations in the Gαs-PKA pathway, with largely endocrine and neoplastic phenotypes. Here, we present a signaling-centric review of Gαs-PKA-driven pathophysiology and integrate computational and structural analysis to identify mutational themes commonly exploited by the Gαs-PKA pathway signalopathies. Major mutational themes include hotspot activating mutations in Gαs, encoded by GNAS, and mutations that destabilize the PKA holoenzyme. With this review, we hope to incite further study and ultimately the development of new therapeutic strategies in the treatment of a wide range of human diseases. SIGNIFICANCE STATEMENT: Little recognition is given to the causative role of Gαs-PKA pathway dysregulation in disease, with effects ranging from infectious disease, endocrine syndromes, and many cancers, yet these disparate diseases can all be understood by common genetic themes and biochemical signaling connections. By highlighting these common pathogenic mechanisms and bridging multiple disciplines, important progress can be made toward therapeutic advances in treating Gαs-PKA pathway-driven disease.

Surgical Treatment of Intramuscular Myxoma

PURPOSE

Intramuscular myxoma (IM) is a rare benign myxoid tumor that may be challenging to differentiate from sarcoma in small amounts of biopsied material. Although IM appears to be well-circumscribed macroscopically, it infiltrates the adjacent edematous muscle microscopically. The recommended treatment is resection, but there is controversy with regard to the appropriate surgical margin. This study aimed to clarify which surgical procedure that should be applied when the preoperative diagnosis is IM and how to manage treatment if the postoperative diagnosis turns out to be a sarcoma.

METHODS

We retrospectively examined 55 IM patients treated from January 1982 to December 2014. Patient characteristics, tumor location, tumor size, radiograph, preoperative and postoperative pathological reports, surgical techniques, treatment outcome, and complications were reviewed. The patients were followed up on for at least 5 years. All patients were confirmed not to have Mazabraud syndrome.

RESULTS

In the 55 IM patients examined, the mean patient age was 48 years and most were female. The most common tumor locations were in the muscles of the thighs (47%) and buttocks (20%). The mean tumor diameter was 5 cm. Wide resection and marginal resection were performed in 24 and 31 patients, respectively. The mean follow-up duration was 19 years. No local recurrence, malignant transformation, or complications were observed.

CONCLUSIONS

Marginal resection is suitable in patients whose preoperative diagnosis is IM, as it is able to prevent local recurrence and allows for the preservation of muscle and muscle fascia. If the postoperative diagnosis turns out to be myxoid sarcoma, minimum surgical contamination makes additional wide resection less invasive.

Pediatric Obturator Internus Muscle Myxoma

Intramuscular myxoma is a rare benign tumor that presents as a slow-growing, deeply seated mass confined within a skeletal muscle. Histologically, these lesions most resemble umbilical cord tissue. They mostly occur in people between 40 and 70 years old, with a 57% female predilection. These tumors are very rare in children. Only one pediatric intramuscular myxoma case is reported in the literature. The goal of this study is to report the case of a 13-year-old girl who presented to our hospital emergency department in 2018 with right hip pain, elevated inflammatory markers, and fever; her initial differential diagnosis was hip septic arthritis, pelvic osteomyelitis, and pelvic abscess. A pelvic MRI revealed a well-defined enhancing round lesion in the right obturator internus muscle. The diagnosis was conformed with a CT-guided core biopsy. The patient's symptoms improved with conservative management, and she continues to be doing well 2 years later. Pediatric pelvic intramuscular myxomas are extremely rare; however, they can have a presentation that mimic a more serious condition such as hip septic arthritis, pelvic osteomyelitis, and pelvic abscess and should be considered in the differential diagnosis in a pediatric patient presenting with hip pain.

Myxoid neoplasms of bone and soft tissue: a pattern-based approach

INTRODUCTION

The accurate diagnosis of musculoskeletal neoplasms is difficult but a pattern-based approach combined with ancillary testing has been shown to improve diagnostic accuracy. The pattern-based approach is particularly appropriate for myxoid lesions.

MATERIALS AND METHODS

The authors reviewed their personal experience of over 3 decades of diagnosing myxoid neoplasms of musculoskeletal lesions.

RESULTS

The authors found that myxoid lesions can be accurately classified based on cell type, nuclear atypia, presence of blood vessel fragments, as well as the results of immunohistochemical and molecular testing.

CONCLUSIONS

Musculoskeletal lesions with a prominence of myxoid or chondroid material in the background can be accurately diagnosed using pattern analysis and ancillary testing.

Oral intramuscular myxoma: case report and brief review of the literature

OBJECTIVE

Myxomas are rare benign mesenchymal soft tissue tumors that seldom affect the head and neck area. The present report describes a rare case of intramuscular myxoma of the oral cavity and briefly reviews the literature regarding the occurrence of these lesions in the maxillofacial area.

STUDY DESIGN

A 59-year-old patient was referred for the development of a slow-growing tumefaction in the right buccal mucosa in the previous 12 months. Magnetic resonance imaging was performed to characterize the lesion's dimensions and its relationship with the surrounding structures, and it revealed intramuscular localization in correspondence with the medial pterygoid muscle. Incisional biopsy was carried out to aid in the final diagnosis.

RESULTS

Histology revealed the presence of an intramuscular myxoma, characterized by discontinuous margins and locally infiltrating muscular fibers. A second surgery was performed to totally remove the lesion. Follow-up at 6 months did not show any signs of recurrence. A literature search was performed to retrieve data on the incidence of oral intramuscular myxomas.

CONCLUSIONS

To the best of our knowledge, this is the first case of intramuscular myxoma of the medial pterygoid muscle reported in the literature. Although rarely encountered, intramuscular myxomas should be considered when performing differential diagnoses of soft tissue masses at the level of the masticatory muscles.

Multiple paraspinal intramuscular myxomas: case report

Intramuscular myxomas (IMMs) are rare benign tumors of mesenchymal origin that are most often located in large skeletal muscles, particularly of the thigh. They have also been reported within the paraspinal musculature and should be considered in the differential diagnosis of a paraspinal mass. These lesions can cause neurological symptoms due to mass effect. This is a report of a 52-year-old man with multiple paraspinal tumors that exhibited concerning growth on serial imaging studies. To the authors' knowledge, this represents the first report of a patient with multiple paraspinal myxomas. CT-guided biopsy followed by surgical excision of the largest mass was performed. Histopathological analysis was consistent with an IMM. Patients with multiple IMMs often have an underlying genetic syndrome such as Mazabraud syndrome, McCune-Albright syndrome, or Carney complex. Despite variable growth patterns and associations with genetic syndromes, multiple IMMs have had no documented cases of malignant transformation into myxoid sarcoma; therefore, surgical excision should be considered based on a patient's individual symptoms.

[Myxoid soft tissue tumours : An algorithm for differential diagnosis]

Soft tissue neoplasms with myxoid features are collectively not uncommon. Their often complex differential diagnosis makes them significantly over-represented among consultation cases. This applies not only to sarcomas but in particular to benign lesions as well. Generally, myxoid soft tissue lesions are divided into two major groups: (1) myxoid lesions by definition (which can however rarely be non-myxoid) and (2) rare myxoid variants of otherwise non-myxoid entities.Four major diagnostic challenges are responsible for the complexity of myxoid soft tissue neoplasms: (1) Diagnosis of malignancy in many cases is not based on conventional malignancy criteria but is defined by the entity itself, making under-diagnosis of malignancy likely in entities such as low-grade fibromyxoid sarcoma. (2) On the other hand, harmless myxoid lesions with features of high proliferation, e.g. nodular and proliferative fasciitis, tend to be over-diagnosed as malignant by the unworried. (3) The necessity to assess not only cellular morphology/differentiation, but also the stromal, vascular and architectural characteristics adds to the complexity of the differential diagnostic algorithm. (4) Last but not least, recognition of unexpected myxoid variants of non-myxoid entities is basically impossible if focal conventional areas are absent, underlining the need for high suspicion index and sufficient sampling.This review illuminates the various aspects related to the differential diagnostic workup of these challenging entities.

[Tumors with predominantly adipocytic morphology]

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