Classification Of Soft Tissue Tumors Research Articles

Superficial ALK-rearranged myxoid spindle cell neoplasms: Clinicopathologic and molecular analysis of two cases and a review of the literature

Superficial anaplastic lymphoma kinase (ALK)-rearranged myxoid spindle cell neoplasms are a recently identified subtype of cutaneous soft tissue tumors, distinct for their co-expression of CD34 and S100 and characterized by ALK gene rearrangements. Although 72 cases have been reported primarily as isolated case reports, this tumor subtype has yet to be included in the WHO classification of soft tissue tumors, underscoring the need for further study. In this study, we diagnosed two additional cases, both arising in the dermis and subcutaneous tissue. These tumors exhibited characteristic pathological features, including linear or concentric whorl patterns, prominent myxoid and collagenized stroma, mild cellular atypia, and rare mitotic activity. The presence of infiltrative margins and the potential for recurrence after surgery suggest at least locally aggressive clinical behavior. Immunohistochemically, the tumors diffusely expressed S100 and CD34, with strong ALK-D5F3 positivity, confirmed by ALK gene rearrangement. These findings further expand the clinical and pathological spectrum of ALK-rearranged neoplasms and highlight the need for continued research on their biological behavior and classification.

Innovations in the classification of soft tissue tumors

Soft tissue tumors are avery heterogeneous group of tumors. Their classification is regularly updated by the World Health Organization (WHO), most recently in 2020. The current classification of soft tissue tumors emphasizes molecular biological tumor characteristics, which enable tumor-specific treatment. In addition to Ewing's sarcoma, which occurs as bone as well as extra-skeletal soft tissue tumors as asmall round cell sarcoma, three other subtypes of undifferentiated, small and round cell sarcomas have been introduced. Some names of the new sarcomas can be derived from the gene mutations. The groups of adipocytic and (myo)fibroblastic tumors have been extended by three further entities. There were further additions to vascular soft tissue tumors, smooth muscle cell tumors, peripheral nerve sheath tumors and tumors of uncertain differentiation. Adistinction is made between benign, intermediate locally aggressive, intermediate rarely metastatic and malignant soft tissue tumors.

The effectiveness of adjuvant therapy in adult patients with spindle cell/sclerosing rhabdomyosarcoma: A single-center retrospective study.

e23550 Background: In recent years, the WHO classification of soft tissue tumours has classified spindle cell/sclerosing rhabdomyosarcoma (RMS) as a novel subtype of RMS. However, the prognosis and standard treatment modalities for operable spindle cell/sclerosing RMS patients remain unclear. This study aims to investigate the effectiveness and influencing factors of postoperative adjuvant therapy in adult patients with spindle cell/sclerosing RMS. Materials and Methods: This single-center retrospective study enrolled adult patients with spindle cell/sclerosing RMS who underwent surgery and subsequent adjuvant therapy at West China Hospital, Sichuan University, from August 2014 to March 2023. The included patients initially underwent surgical excision, followed by one of the adjuvant treatments: radiotherapy, chemotherapy, or a combination of radiotherapy and chemotherapy. Disease-Free Survival (DFS) and Overall Survival (OS) were calculated for the included patients in this study. Univariate analysis and multivariate COX regression were conducted to determine prognostic factors. Results: This study included a total of 17 patients diagnosed with spindle cell/sclerosing RMS. Among them, 10 (58.8%) patients received postoperative adjuvant chemoradiotherapy, while 7 (41.2%) patients underwent postoperative chemotherapy alone. 12 (70.6%) patients received chemotherapy following the VAC regimen, and 5 (29.4%) patients received non-VAC chemotherapy. The prognosis analysis indicates that the median DFS was not reached, with a 1-year DFS rate of approximately 87.8% and a 2-year DFS rate of approximately 52.4%. The median OS was not reached, with a 1-year OS rate of 100% and a 2-year OS rate of approximately 92.9%. Univariate analysis shows that compared to undergoing non-R0 resection, undergoing R0 surgical resection significantly improves patient DFS (P = 0.02). Compared to no postoperative radiotherapy, receiving postoperative prophylactic radiotherapy significantly improved both DFS (P = 0.01) and OS (P = 0.02). In contrast, using VAC as adjuvant chemotherapy did not significantly increase DFS and OS compared to non-VAC regimens (P = 0.83 and 0.57, respectively). Multivariate Cox regression analysis demonstrated that the receipt of postoperative prophylactic radiotherapy independently predicted DFS (P = 0.03). Conclusions: In adult patients with spindle cell/sclerosing RMS, R0 resection, when compared with non-R0 resection, delays disease recurrence but does not enhance overall survival. Long-term outcomes may be improved in patients who receive postoperative adjuvant radiotherapy. However, choosing a VAC regimen as adjuvant chemotherapy may not contribute to an improved long-term prognosis when compared with a non-VAC regimen. Keywords: adjuvant therapy, spindle cell, sclerosing, rhabdomyosarcoma, effectiveness

A Case Report of Superficial Solitary Fibrous Tumor in the Right Parotideomasseteric Region.

Solitary fibrous tumors (SFTs) are rare mesenchymal tumors that occur in various soft tissues and organs throughout the body. Superficial SFTs in the head and neck region are uncommon and reports of such cases are limited. An elderly Japanese woman in her 80s presented to our clinic with a smooth mass in the right parotideomasseteric region. Ultrasonography and magnetic resonance imaging revealed a well-defined subcutaneous mass measuring 20 mm. For a definitive diagnosis and treatment, surgical resection was performed under local anesthesia. Intraoperatively, a brown-colored tumor was identified beneath the skin, without surrounding tissue adhesion, and was completely excised. Immunohistochemistry, revealing the expression of STAT6, confirmed the diagnosis of SFT. Based on the SFT risk classification, this case was classified into the low-risk group, and no recurrence occurred during the 4 year postoperative period. According to the 2020 World Health Organization Classification of Soft Tissue Tumors, SFTs belong to the intermediate category with recurrence potential. In previous studies, cases of positive margins and recurrence have been reported in superficial SFTs, and SFTs may show benign features on clinical presentation but require precise surgical manipulation. Therefore, it is crucial for otolaryngologists to gain a comprehensive understanding of this tumor for appropriate treatment.

Primitive myxoid mesenchymal tumor of infancy, an enigmatic entity: A case report.

Primitive myxoid mesenchymal tumor of infancy (PMMTI) is a rare soft tissue neoplasm of intermediate malignant potential occurring predominantly in infants and younger children. It can show aggressive local infiltration of surrounding structures and frequent relapses but rare metastasis. Morphologically, it is characterized by a proliferation of immature mesenchymal cells in a myxoid background with mild cytologic atypia and branching vessels. The tumor cells demonstrate immunoreactivity with vimentin and BCOR, however, are negative for more specific lineage markers. Its molecular hallmark is BCOR-internal tandem duplication. Previously classified as infantile fibrosarcoma/undifferentiated sarcoma, the association with BCOR-ITD has led to its reclassification as part of a distinct entity-"Sarcoma with BCOR Genetic Alterations"-in the 2020 WHO Classification of Soft Tissue Tumours. Here is a report of a case of a 2-year-old boy with a recurrent scalp mass identified as a primitive myxoid mesenchymal tumor of infancy.

Clinicopathological Features of Primary Renal Mesenchymal Neoplasms in Adults: A Cross-sectional Study

Introduction: Renal mesenchymal tumours are a subset of primary renal tumours arising from the mesenchymal tissue in the kidney. They are a heterogeneous group of mostly benign tumours that exhibit varied behaviours and molecular characteristics. Aim: To analyse the wide spectrum of histological subtypes, their unique clinical presentation, and pathological features of primary renal mesenchymal neoplasms. Materials and Methods: This was a retrospective crosssectional observational clinicopathological study conducted in Department of General Pathology, Christian Medical College, tertiary care hospital, Vellore, Tamil Nadu, India, looking at data of adult Primary Renal Mesenchymal Tumours (PRMT) for a 15- year period between January 2006 and March 2021. Clinical details such as age, presenting symptoms, and tumour size were obtained from the hospital information system. Histopathology and immunohistochemical slides were reviewed for all the cases. Additional Immunohistochemistry (IHC) and molecular studies were performed for the undifferentiated sarcomas. The tumours were categorised into three groups as recommended by the World Health Organisation (WHO) 2020 classification of soft-tissue tumours based on biological behaviour: benign, intermediate, and malignant. Continuous variables are expressed as mean and Standard Deviation (SD). Comparison of categorical variables between groups was performed using the Chi-squared test. Continuous variables between groups were compared using the Student’s t-test for significance. A p-value of less than 0.05 was considered statistically significant. Results: Of the 2164 nephrectomies performed for neoplastic conditions, 97 (4.5%) were diagnosed as renal mesenchymal tumours. There were 59 (60.8%) benign, 10 (10.3%) with intermediate biologic behaviour and 28 (28.9%) malignant tumours. The mean ages at presentation were 40.5 years for benign, 43.4 years for intermediate, and 41 years for malignant tumours, respectively. Haematuria was seen in 11 of 38 (29%) intermediate grade and malignant tumours and in only 6 of 59 (10%) benign tumours, a difference that was statistically significant (p-value=0.017). Malignant tumours 24 of 28 (86%) were more likely to be larger (>7 cm) when compared to benign tumours 28 of 59 (47%) at the time of presentation (p-value=0.027). Classical angiomyolipomas constituted 53/59 (90%) of the benign tumours. Of the 10 intermediate grade tumours, epithelioid angiomyolipomas and solitary fibrous tumours were the most common, accounting for 50% and 30% of the intermediate group, respectively. Undifferentiated small round cell sarcoma was the most common malignant neoplasm, making up 12/28 (43%) of the malignant tumours. Conclusion: The present study found that renal mesenchymal tumours constitute a small but unique group of renal tumours. They are predominantly benign, but up to a quarter are malignant. Malignant tumours tend to be larger and more often present with haematuria. The present study highlights the importance of IHC in the diagnosis of intermediate and malignant mesenchymal tumours and the requirement of exhaustive molecular studies individually tailored to the immuno-profile of malignant tumours.

Diagnostics and Treatment of Extrameningeal Solitary Fibrous Tumors.

Solitary fibrous tumors (SFT) are rare mesenchymal neoplasms that account for less than 2% of all soft tissue masses. In the latest WHO 2020 Classification of Soft Tissue Tumors, extrameningeal SFT was listed as intermediate (rarely metastasizing) or malignant neoplasms. Due to the lack of characteristic clinical features, their diagnosis and treatment remain challenging. The pathogenesis of SFT is often associated with the presence of fusions of the NAB2-STAT6 gene on the 12q13 chromosome. Cytoplasmic CD34 positive staining is considerably characteristic for most SFTs; less frequently, factor XII, vimentin, bcl-2, and CD99 are present. A key factor in the diagnosis is the prevalent nuclear location of STAT6 expression. Radical resection is the mainstay of localized SFTs. In the case of unresectable disease, only radiotherapy or radio-chemotherapy may significantly ensure long-term local control of primary and metastatic lesions. To date, no practical guidelines have been published for the treatment of advanced or metastatic disease. Classical anthracycline-based chemotherapy is applicable. The latest studies suggest that antiangiogenic therapies should be considered after first-line treatment. Other drugs, such as imatinib, figitumumab, axitinib, and eribulin, are also being tested. Definitive radiotherapy appears to be a promising therapeutic modality. Since standards for the treatment of advanced and metastatic diseases are not available, further investigation of novel agents is necessary.

Primary CIC-rearranged Gastric sarcoma: A rare diagnosis

Gastric sarcoma is rare, accounting for 1-3% of all gastric neoplasms. WHO has published a new classification of soft tissue tumors and a group of undifferentiated round cell sarcomas, including CIC-rearranged sarcoma has been added. CIC-rearranged sarcoma has not been reported till date. We report a case of CIC-rearranged gastric sarcoma which was managed with chemotherapy and multivisceral resection.

Assessment of The Utility of The Sarcoma DNA Methylation Classifier In Surgical Pathology.

Diagnostic classification of soft tissue tumors is based on histology, immunohistochemistry, genetic findings, and radiologic and clinical correlations. Recently, a sarcoma DNA methylation classifier was developed, covering 62 soft tissue and bone tumor entities. The classifier is based on large-scale analysis of methylation sites across the genome. It includes DNA copy number analysis and determines O 6 methylguanine DNA methyl-transferase methylation status. In this study, we evaluated 619 well-studied soft tissue and bone tumors with the sarcoma classifier. Problem cases and typical examples of different entities were included. The classifier had high sensitivity and specificity for fusion sarcomas: Ewing, synovial, CIC -rearranged, and BCOR -rearranged. It also performed well for leiomyosarcoma, malignant peripheral nerve sheath tumors (MPNST), and malignant vascular tumors. There was low sensitivity for diagnoses of desmoid fibromatosis, neurofibroma, and schwannoma. Low specificity of matches was observed for angiomatoid fibrous histiocytoma, inflammatory myofibroblastic tumor, Langerhans histiocytosis, schwannoma, undifferentiated sarcoma, and well-differentiated/dedifferentiated liposarcoma. Diagnosis of lipomatous tumors was greatly assisted by the detection of MDM2 amplification and RB1 loss in the copy plot. The classifier helped to establish diagnoses for KIT-negative gastrointestinal stromal tumors, MPNSTs with unusual immunophenotypes, and undifferentiated melanomas. O 6 methylguanine DNA methyl-transferase methylation was infrequent and most common in melanomas (35%), MPNSTs (11%), and undifferentiated sarcomas (11%). The Sarcoma Methylation Classifier will likely evolve with the addition of new entities and refinement of the present methylation classes. The classifier may also help to define new entities and give new insight into the interrelationships of sarcomas.

Angioleiomyoma of the Sinonasal Tract: A Systematic Review of an Uncommon Clinicopathological Entity.

Introduction Angioleiomyoma is a rare neoplasm that represents ∼ 0.2 % of all head and neck benign tumors and ∼ 2% of total cases of tumors of the sinonasal tract. It was once considered a possible subtype of leiomyoma, but, in the 2020 World Health Organization (WHO) classification of soft tissue tumors, it is accepted as a singular entity. Objective To systematically review the existing literature on angioleiomyoma in the light of the new classification of soft tissue tumors. Data Synthesis The present study was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. A comprehensive search in the PubMed, Cochrane, Scopus, and Google Scholar databases was performed in January 2022. The search items included the following keywords: nasal angioleiomyoma OR sinonasal angioleiomyoma OR nasal vascular leiomyoma OR sinonasal vascular leiomyoma . A total of 87 patients were evaluated. He age of the patients in the studies ranged from 15 to 88 years (mean age at diagnosis: 55.6 years). The most common site of involvement was the nasal septum (28.4 %), followed by the inferior turbinate (22.5%). The most common symptom was nasal obstruction (66.7%), followed by epistaxis (47.1%). Surgical excision represented the main treatment, and there was recurrence of pathology in only 1 case (0.9%). Conclusion To our knowledge, only 87 cases of sinonasal-tract angioleiomyoma have been previously described. The results of the present review seem to confirm the rarity and the benign nature of this neoplasm, and they seem to confirm the necessity to improve the available data about sinonasal-tract angioleiomyoma.

Clinicopathological and treatment response characteristics of updated rhabdomyosarcoma histomolecular subtypes: An Asian population-based study.

New histomolecular subtypes of rhabdomyosarcoma have recently been defined but their corresponding clinical characteristics are not well described. Also, these clinical phenotypes vary greatly by age and ethnicity but have not been profiled in Asian populations. Thus, we sought to determine the landscape of rhabdomyosarcoma subtypes in a national Asian cohort and compare clinical characteristics among age groups and molecular subtypes. We performed a retrospective population-based study of all rhabdomyosarcoma patients in Singapore public hospitals from 2004 to 2014 (n=67), and assigned histomolecular subtypes according to the updated 2020 WHO classification of soft tissue tumors following central pathology review and molecular profiling. Age-specific prevalence followed a tri-modal peak. There were significantly more embryonal and alveolar (p=0.032) and genitourinary (non-bladder/prostate) tumors (p=0.033) among children. Older age was associated with complete resection among spindle cell/sclerosing tumors (p=0.027), with the omission of chemotherapy among embryonal tumors (p=0.001), and with poorer survival among embryonal and alveolar tumors (p=0.026, p=0.022, respectively). Overall survival differed with stage, group, and surgical resection, adjusted for age group (p=0.004, p=0.001, p=0.004, respectively). Spindle-cell/sclerosing tumors showed an indolent phenotype with a significantly lower incidence of nodal metastasis (p=0.002), but two of 15 patients with MYOD1 mutations had a contrastingly aggressive disease. Disease and treatment response profiles of rhabdomyosarcoma subtypes vary significantly between adults and children, especially surgical resectability. In our Asian population, poorer outcomes were observed in adults with embryonal and alveolar tumors, while activating mutations influence the behavior of otherwise favorable spindle cell/sclerosing tumors.

Morphological variations of two cases of maxillary myofibromas

The aim of this case report is to depict the varied spectrum of clinical presentation of two cases of solitary myofibromas, one of which was intra-osseous whilst the other presented as a soft tissue lesion. This highlights the spectrum of the clinical presentation of the same pathology. In the most recent World Health Organisation (WHO) 2022 classification of soft tissue tumours, myofibroma is included under the category of myopericytomas. Myopericytoma is a distinctive perivascular myoid neoplasm that forms a morphological spectrum with myofibroma. Molecular evidence has revealed PDGFRB (platelet-derived growth factor receptor beta) mutations in myopericytoma and myofibroma as well as SRF-RELA gene fusions in both lesions confirming a common pathogenesis for both.1 Myofibromas are benign soft tissue neoplasms derived from myofibroblastic cells.2 The term myofibroma refers to a solitary lesion. Myofibromatosis refers to cases in which multiple lesions are present which may affect either one or multiple anatomical locations. Myofibromatosis is almost exclusively seen in young children under the age of 2-years. Myofibromas exhibit a wide age range of clinical presentation and may be present at birth or arise within the first two years of age, but may also present in adults with a significant male predominance. Solitary myofibromas have a predilection to occur in the oral cavity, skin or subcutis of the head, neck and trunk.

Recurrent Giant Myofibroblastic Sarcoma of Neck in a Teenager: Overcoming Treatment Challenges

Sarcomas are rare tumors arising from a variety of mesenchymal tissues which are even rarer in head and neck region amounting 1% only of the 5% of sarcomas. About 80% of head and neck sarcomas originate in soft tissue while the remaining 20% arise from bone (Cormier and Pollock in J Clin 54:94−109, 2004). One among the commonly presenting variants of sarcomas in head and neck that our patient was diagnosed with is Low grade myofibroblastic sarcoma (LGMS). These even though uncommon have a predilection for head and neck region particularly the tongue (Mentzel et al. in Am J Surg Pathol 22:1228−38, 1998; Cai et al. in Virchows Arch 463:827−36, 2013; Meng et al. in Chin Med J 120:363–9, 2007; Demarosi et al. in Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 108:248–54, 2009). LGMS was reclassified as a distinct entity by the WHO classification of soft tissue tumors in 2002 (Qiu et al. in Oncol Lett 9:619−25, 2015). Oncological resection is the mainstay of treatment. In case of bulky tumor, resection and reconstruction would be challenging. We report a recurrent LGMS of 15-year-old girl who presented with a ginormous soft tissue swelling in her left neck region which made her day-to-day activities strenuous and made her non ambulatory and the line of treatment executed in order to get her back on feet, healthy & free of the debilitating tumor.

Atypical spindle cell/pleomorphic lipomatous tumour (ASPLT): A report of three FNA cases and comparison with spindle cell/pleomorphic lipoma cytopathology.

Atypical spindle cell/pleomorphic lipomatous tumour (ASPLT) is an infrequently appreciated benign lipomatous neoplasm newly accepted into the most recent WHO classification of soft tissue tumours. Our cytopathology files were searched for examples of ASPLT and spindle cell/pleomorphic lipoma (SCPL) having histopathological verification. Conventional fine needle aspiration (FNA) biopsy smears were performed using standard techniques. Eleven patients including three cases of ASPLT and eight of SCPL (M:F=4.5:1; age range: 39-97 years, mean age=60 years) met the inclusion criteria. FNA biopsy sites included extremity (5, 45%), trunk (3, 27%), and head/neck (3, 27%). All aspirates were from primary neoplasms. FNA diagnoses of ASPLT cases were spindle cell lipomatous neoplasm, fibrotic low-grade SC neoplasm, and myxoid lipomatous neoplasm. Eight SCPL cases were diagnosed as spindle cell neoplasm (3), spindle cell lipoma (SCL) (1), pleomorphic lipoma (1), suspicious for SCL (1), benign adipose tissue (1), and benign spindle cells and connective tissue (1). Ancillary testing in two ASPLT cases showed positive CD34 and negative MDM2 immunostain in one, and negative FISH results for MDM2 and DDIT3 in another. ASPLT is a novel lipomatous neoplasm simulating primarily SCPL and atypical lipoma/well-differentiated liposarcoma. Diligent cytomorphological observation, clinical information, and ancillary testing may allow for its specific recognition using FNA biopsy.

Sarcoma of the right femur with heterogeneous morphology similar to myoepithelial carcinoma and amplification of the EWSR1 gene in a 14-year-old boy. Clinical observation and literature review

Ewing sarcoma (ES) is one of the most frequent primary bone tumors and has a well-studied diagnostically important genetic background. However, there are primary bone round-cell tumors with atypical morphology different from conventional ES, tumors with rearrangement of the EWSR1 gene with partner genes not from the ETS gene family, tumors with unusual changes in the EWSR1 gene (amplification or deletion), which can cause significant diagnostic difficulties. In this article, we will describe a case of a primary bone tumor with an atypical morphology similar to myoepithelial carcinoma, where an amplification of the EWSR1 gene was detected. According to morphological, immunological, genetic and clinical signs, this tumor was classified as a sarcoma from the EWSR1::non-ETS group of round-cell sarcomas, namely a sarcoma with EWSR1::NFATC2 rearrangement, first formalized in the WHO classification of soft tissue tumors in 2020.

Changes in the WHO classification (2020) of soft tissue tumors

The article provides an overview of the main changes in the current (2020) WHO classification of soft tissue tumors, as well as selected updates that have occurred since the release of the classification.

Histopathological evaluation of benign soft tissue lesions at Nnamdi Azikiwe University teaching hospital, Nnewi, south-east Nigeria: A 9-year review

Background: Soft tissue lesions are remarkably diverse and range from inflammatory, self-limited lesions to neoplasm. The diversity of these lesions frequently poses a diagnostic challenge to pathologists and remains a subject of interests. Lack of research on soft tissues in our setting has prompted the need to study them. Objectives: The aim of this study was to determine the benign lesions of soft tissues with respect to age, sex, anatomic site, and histologic types. It also aimed to determine the baseline data of benign soft tissue lesions in Nnewi, Nigeria. Materials and Methods: This study reviewed all histologically diagnosed benign soft tissue lesions at the Histopathology Department of Nnamdi Azikiwe University Teaching Hospital (NAUTH), Nnewi, Nigeria from 2011 to 2019 and classified the tumors using the 2020 WHO Classification of Soft Tissue Tumours. Results: A total of 351 cases of soft tissue lesions were diagnosed during the study period, out of which 251 were benign lesions and accounted for 71.5% (251/351) of all soft tissue lesions, whereas 28.5% (100/351) of the cases were malignant. The benign lesions included inflammatory and benign neoplasm, of which neoplasm accounted for the majority of the cases with a frequency of 94.0% (236/251), whereas inflammatory lesions accounted for 5.9% (15/251). The 236 benign soft tissue tumors diagnosed had a male-to-female ratio of 1: 1.4 with a mean age (SD) of 37.5 (19.5) years. The most frequent occurrence of benign tumors was seen in the fourth decade with 52 cases (21.0%), followed by fifth decade with 42 cases (16.7%). Adipocytic tumors were the commonest with a frequency of 54.0% (135/251), followed by peripheral nerve sheath tumors (PNSTs) with 12.4% (31/251) and then vascular and fibroblastic/myofibroblastic tumors with 10.8% (27/251) and 5.6% (14/251), respectively. Lipoma is the most common histologic type of benign soft tissue tumor and the only benign adipocytic tumor. This is followed by hemangioma 9.6% (24/251) and then neurofibroma 7.6% (19/251). Lipoma accounted for 37.09% (135/351) of all soft tissue lesions and the majority of them were seen in the fourth decade, whereas hemagioma and neurofibroma occurred more at the first decade. The most common anatomic distributions of these benign tumors were lower extremities with 23.5% (n = 59/251), followed by trunk 21.1% (n = 53). The major inflammatory lesions were tuberculoid granulomatous inflammation and panniculitis with 2.3% (6/251) of cases each. Others were necrotizing fasciitis (n = 2) and eosinophilic myositis (n = 1). Conclusion: Benign soft tissue tumors had a slight female preponderance. Lipoma is the single most common benign soft tissue neoplasm, whereas tuberculosis and panniculitis were the two most common inflammatory soft tissue lesions. Histopathological evaluation of these lesions still stands as a gold standard in their diagnosis.

Malignant Melanotic Nerve Sheath Tumors: A Review of Clinicopathologic and Molecular Characteristics.

Malignant melanotic nerve sheath tumor (MMNST) which was formerly known as melanocytic schwannoma, is an uncommon aggressive type of nerve sheath tumor. It originates from nerve roots with clonal Schwann cell proliferation and melanin pigment production. MMNST which was once thought to be a benign tumor is now considered a malignant disease based on the latest 2020 World Health Organization classification of soft tissue tumors. Interestingly, despite the histologic features appearing benign with a low proliferation index, the clinical course of this tumor is malignant, which was demonstrated in case series with high rate of recurrences and metastasis. This tumor can occur sporadically or in patients with an underlying familial predisposition syndrome called, Carney's complex. Affected patients will often harbor a germline mutation in the PRKAR1A gene. MMNST can be histologically difficult to distinguish from malignant melanoma, other melanocytic tumors, and Schwannoma. Having a better understanding of its clinic pathologic characteristics and associated conditions is essential in properly diagnosing and managing affected individuals. This includes the possible need for genetic testing to detect germline mutations, genetic counseling, and surveillance according to published recommendations. In this article, we summarize the clinic pathologic and molecular features of MMNST and discuss what is known about its molecular biology and its associations with predisposing conditions. The review was conducted through an extensive PubMed search using keywords then relevant publications were selected.

NTRK-rearranged spindle cell neoplasms are ubiquitous tumours of myofibroblastic lineage with a distinct methylation class.

NTRK gene fusions have been described in a wide variety of central nervous system (CNS) and soft tissue tumours, including the provisional tumour type 'spindle cell neoplasm, NTRK-rearranged' (SCN-NTRK), added to the 2020 World Health Organisation Classification of Soft Tissue Tumours. Because of histopathological and molecular overlaps with other soft tissue entities, controversy remains concerning the lineage and terminology of SCN-NTRK. This study included 16 mesenchymal tumours displaying kinase gene fusions (NTRK fusions and one MET fusion) initially diagnosed as infantile fibrosarcomas (IFS), SCN-NTRK and adult-type fibrosarcomas from the soft tissue, viscera and CNS. We used immunohistochemistry, DNA methylation profiling, whole RNA-sequencing and ultrastructural analysis to characterise them. Unsupervised t-distributed stochastic neighbour embedding analysis showed that 11 cases (two CNS tumours and nine extra-CNS) formed a unique and new methylation cluster, while all tumours but one, initially diagnosed as IFS, clustered in a distinct methylation class. All the tumours except one formed a single cluster within the hierarchical clustering of whole RNA-sequencing data. Tumours from the novel methylation class co-expressed CD34 and S100, had variable histopathological grades and frequently displayed a CDKN2A deletion. Ultrastructural analyses evidenced a myofibroblastic differentiation. Our findings confirm that SCN-NTRK share similar features in adults and children and in all locations combine an infiltrative pattern, distinct epigenetic and transcriptomic profiles, and ultrastructural evidence of a myofibroblastic lineage. Further studies may support the use of new terminology to better describe their myofibroblastic nature.

Huge Primary Intermediate-grade Myofibroblastic Sarcoma in the Retroperitoneum.

Myofibroblastic sarcoma is exceedingly rare, with low-grade features in most cases, and rarely involves the retroperitoneum. The 2020 World Health Organization (WHO) classification of soft tissue tumours still lists only low-grade myofibroblastic sarcoma and shows no consensus on the definitions of high- and intermediate-grade myofibroblastic sarcomas, in contrast to the 2013 WHO classification. Surgical resection of the tumour and adjacent structures is the standard of care for most patients, and intermediate- and high-grade myofibroblastic sarcomas have very poor survival. We describe a patient with intermediate-grade myofibroblastic sarcoma in the retroperitoneum, who underwent en bloc resection and ureteroplasty without adjuvant therapy and was free of pain and any other discomfort during 19 months of follow-up. Key Words: Myofibroblastic sarcoma, Intermediate grade, Retroperitoneum, Surgery.