Clinicopathologic features of 300 rhabdomyosarcomas with emphasis upon differential expression of skeletal muscle specific markers in the various subtypes: A single institutional experience

PAX fusion proteins deregulate gene networks controlling mitochondrial translation in pediatric rhabdomyosarcoma

Alveolar rhabdomyosarcoma (ARMS) patients harboring PAX3-FOXO1 and PAX7-FOXO1 fusion proteins exhibit a greater incidence of tumor relapse, metastasis, and poor survival outcome, thereby underscoring the urgent need to develop effective therapies to treat this subtype of childhood cancer. To uncover mechanisms that contribute to tumor initiation, we developed a novel muscle progenitor model and used epigenomic approaches to unravel genome re-wiring events mediated by PAX3/7 fusion proteins. Importantly, these regulatory mechanisms are conserved across established ARMS cell lines, primary tumors, and orthotopic-patient derived xenografts. Among the key targets of PAX3- and PAX7-fusion proteins, we identified a cohort of oncogenes, FGF receptors, and genes essential for mitochondrial metabolism and protein translation, which we successfully targeted in preclinical trials. Our data suggest an explanation for the relative paucity of recurring mutations in this tumor, provide a compelling list of actionable targets, and suggest promising new strategies to treat this tumor.

Case report: Lymph node metastasis of pelvic alveolar rhabdomyosarcoma diagnosed by fine needle aspiration cytology

Rhabdomyosarcoma (RMS) is a common soft tissue malignant tumor, especially in young patients. Alveolar rhabdomyosarcoma (ARMS) is a subtype of RMS that is prevalent in adolescents. This malignant tumor usually develops in the extremities and can also involve the trunk, perineum, and pelvis. Now, we report a rare case of pelvic lymph node metastatic alveolar RMS in a young patient, which was determined by fine needle aspiration cytology (FNAC). To the best of our knowledge, this is the first case in which the definite diagnosis of ARMS was initially made by FNAC.

Spindle cell rhabdomyosarcomas: With TFCP2 rearrangements, and novel EWSR1::ZBTB41 and PLOD2::RBM6 gene fusions. A study of five cases and review of the literature

AIMS

Spindle-cell/sclerosing rhabdomyosarcomas (SS-RMS) are clinically and genetically heterogeneous. They include three well-defined molecular subtypes, of which those with EWSR1/FUS::TFCP2 rearrangements were described only recently. This study aimed to evaluate five new cases of SS-RMS and to perform a clinicopathological and statistical analysis of all TFCP2-rearranged SS-RMS described in the English literature to more comprehensively characterize this rare tumour type.

METHODS AND RESULTS

Cases were retrospectively selected and studied by immunohistochemistry, fluorescence in situ hybridization with EWSR1/FUS and TFCP2 break-apart probes, next-generation sequencing (Archer FusionPlex Sarcoma kit and TruSight RNA Pan-Cancer Panel). The PubMed database was searched for relevant peer-reviewed English reports. Five cases of SS-RMS were found. Three cases were TFCP2 rearranged SS-RMS, having FUSex6::TFCP2ex2 gene fusion in two cases and triple gene fusion EWSR1ex5::TFCP2ex2, VAX2ex2::ALKex2 and VAX2intron2::ALKex2 in one case. Two cases showed rhabdomyoblastic differentiation and spindle-round cell/sclerosing morphology, but were characterized by novel genetic fusions including EWSR1ex8::ZBTB41ex7 and PLOD2ex8::RBM6ex7, respectively. In the statistical analysis of all published cases, CDKN2A or ALK alterations, the use of standard chemotherapy and age at presentation in the range of 18-24 years were negatively correlated to overall survival.

CONCLUSION

EWSR1/FUS::TFCP2-rearranged SS-RMS is a rare rhabdomyosarcoma subtype, affecting predominantly young adults with average age at presentation 34 years (median 29.5 years; age range 7-86 years), with a predilection for craniofacial bones, rapid clinical course with frequent bone and lung metastases, and poor prognosis (3-year overall survival rate 28%).

Unraveling the Clinicopathological Diversity and Subtypes of Rhabdomyosarcoma: A Study From a Tertiary Care Center

Background and objective Rhabdomyosarcoma (RMS) is a rare and malignant mesenchymal tumor characterized by skeletal muscle differentiation. While it is a common soft tissue sarcoma in children, its incidence significantly decreases with advancing age, rendering it exceptionally rare in individuals aged more than 45 years. This study aimed to shed light on the clinicopathological diversity and subtypes of RMS, thereby providing a comprehensive overview for enabling diagnostic precision and therapeutic strategies in treating this infrequently encountered malignancy in adults. Methodology This was a hospital-based cross-sectional study conducted in the Department of Pathology. Patients who were diagnosed with RMS over a period of three years were included in the study. The demographic features such as age and sex and aspects related to the tumor site, size, subtypes of RMS, and immunohistochemical expression were studied. Results A total of 14 cases were included in our study. The age at diagnosis ranged from four months to 65 years with a male-to-female ratio of 1:2.5. The sites of presentation were head and neck, trunk, pelvis, genitourinary tract, and retroperitoneum. The histological types were embryonal, alveolar, pleomorphic, and mixed and spindle cell types. The tumor cells were positive for immunohistochemistry markers desmin, MyoD1, and vimentin. Conclusion This study delved into the clinicopathological intricacies of RMS, offering comprehensive insights into its diverse subtypes. Our findings underscore the unique presentation of RMS in adults, with trunk and genitourinary tracts emerging as primary sites and alveolar and pleomorphic RMS observed as the predominant histological subtypes. Furthermore, the study sheds light on rare subtypes with distinct anatomical distributions.

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.

Detection of various fusion genes by one-step RT-PCR and the association with clinicopathological features in 242 cases of soft tissue tumor

Introduction: Over the past decades, an increasing number of chromosomal translocations have been found in different STSs, which not only has value for clinical diagnosis but also suggests the pathogenesis of STS. Fusion genes can be detected by FISH, RT-PCR, and next-generation sequencing. One-step RT-PCR is a convenient method to detect fusion genes with higher sensitivity and lower cost. Method: In this study, 242 cases of soft tissue tumors were included, which were detected by one-step RT-PCR in multicenter with seven types of tumors: rhabdomyosarcoma (RMS), peripheral primitive neuroectodermal tumor (pPNET), synovial sarcoma (SS), myxoid liposarcomas (MLPS), alveolar soft part sarcoma (ASPS), dermatofibrosarcoma protuberans (DFSP), and soft tissue angiofibroma (AFST). 18 cases detected by one-step RT-PCR were further tested by FISH. One case with novel fusion gene detected by RNA-sequencing was further validated by one-step RT-PCR. Results: The total positive rate of fusion genes was 60% (133/213) in the 242 samples detected by one-step RT-PCR, in which 29 samples could not be evaluated because of poor RNA quality. The positive rate of PAX3-FOXO1 was 88.6% (31/35) in alveolar rhabdomyosarcoma, EWSR1-FLI1 was 63% (17/27) in pPNET, SYT-SSX was 95.4% in SS (62/65), ASPSCR1-TFE3 was 100% in ASPS (10/10), FUS-DDIT3 was 80% in MLPS (4/5), and COL1A1-PDGFB was 66.7% in DFSP (8/12). For clinicopathological parameters, fusion gene status was correlated with age and location in 213 cases. The PAX3-FOXO1 fusion gene status was correlated with lymph node metastasis and distant metastasis in RMS. Furthermore, RMS patients with positive PAX3-FOXO1 fusion gene had a significantly shorter overall survival time than those patients with the negative fusion gene. Among them, the FISH result of 18 cases was concordant with one-step RT-PCR. As detected as the most common fusion types of AHRR-NCOA2 in one case of AFST were detected as negative by one-step RT-PCR. RNA-sequencing was used to determine the fusion genes, and a novel fusion gene PTCH1-PLAG1 was found. Moreover, the fusion gene was confirmed by one-step RT-PCR. Conclusion: Our study indicates that one-step RT-PCR displays a reliable tool to detect fusion genes with the advantage of high accuracy and low cost. Moreover, it is a great tool to identify novel fusion genes. Overall, it provides useful information for molecular pathological diagnosis and improves the diagnosis rate of STSs.

The Recent Advances in Molecular Diagnosis of Soft Tissue Tumors

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

Orbital leiomyoma presenting as inverse globe retraction syndrome: a unique presentation of a rare disease

Inverse globe retraction syndrome is a rare ocular motility disorder characterized by limited abduction, with globe retraction and up- or downshoots on attempted abduction, differentiating it from globe retraction due to Duane retraction syndrome, seen on attempted adduction. It can be congenital or acquired. We report the case of a 3-year-old girl who presented with classical features of inverse globe retraction syndrome secondary to an underlying orbital tumor involving the medial rectus muscle. Incisional biopsy confirmed the diagnosis of a leiomyoma. At 10 months' follow-up, vision, ocular alignment, and ocular motility had improved.

Pax3 loss of function delays tumour progression in kRAS-induced zebrafish rhabdomyosarcoma models

Rhabdomyosarcoma is a soft tissue cancer that arises in skeletal muscle due to mutations in myogenic progenitors that lead to ineffective differentiation and malignant transformation. The transcription factors Pax3 and Pax7 and their downstream target genes are tightly linked with the fusion positive alveolar subtype, whereas the RAS pathway is usually involved in the embryonal, fusion negative variant. Here, we analyse the role of Pax3 in a fusion negative context, by linking alterations in gene expression in pax3a/pax3b double mutant zebrafish with tumour progression in kRAS-induced rhabdomyosarcoma tumours. Several genes in the RAS/MAPK signalling pathway were significantly down-regulated in pax3a/pax3b double mutant zebrafish. Progression of rhabdomyosarcoma tumours was also delayed in the pax3a/pax3b double mutant zebrafish indicating that Pax3 transcription factors have an unappreciated role in mediating malignancy in fusion negative rhabdomyosarcoma.

Embryonal Rhabdomyosarcoma of the Uterine Cervix: A Clinicopathologic Study of 94 Cases Emphasizing Issues in Differential Diagnosis Staging, and Prognostic Factors

Embryonal rhabdomyosarcoma of the uterine cervix (cERMS) is rare and frequently associated with DICER1 mutations. We report 94 tumors that arose in patients aged 7 to 59 (median=23) years and presented with vaginal bleeding (52), protruding vaginal mass (17), cervical polyp (8), or expelled tumor fragments per vagina (5). Nine had DICER1 syndrome, 8 of whom had other syndromic manifestations including ovarian Sertoli-Leydig cell tumor (7), multinodular goiter (3), pleuropulmonary blastoma (2), pineoblastoma (1), and osteosarcoma (1). Syndromic patients were younger than nonsyndromic patients (16 vs. 24 y). Tumor size ranged from 2 to 24 (median=4.5) cm. Ninety-two tumors were polypoid, most being grape-like (77 of 92). They were characterized by aggregates of primitive cells, almost always exhibiting a cambium layer, within a variably myxoedematous stroma and were hypocellular (63), moderately cellular (22), or hypercellular (9). Entrapped glands, typically scant, were present in 84 tumors. Primitive hyperchromatic ovoid to spindled cells with minimal cytoplasm predominated but differentiated rhabdomyoblasts with abundant eosinophilic cytoplasm (having cross-striations in 30) were seen in 83 tumors; they were often sparse but predominated in three. Nine tumors showed areas of intersecting fascicles and 4 zones with densely cellular (solid) growth. Cartilage was present in 38. Anaplasia was seen in 15 tumors, as was necrosis. Mitotic activity ranged from 1 to 58/10 high-power fields (median=8). The varied microscopic features resulted in a spectrum of differential diagnostic considerations, mainly typical and cellular forms of fibroepithelial polyps, Mullerian adenosarcoma, and other sarcomas. Follow-up was available for 79 patients ranging from 6 to 492 (median=90) months. Treatment information was available in 62 and included polypectomy in 6 patients (2 also received chemotherapy), limited resection in 26 (14 also received chemotherapy), hysterectomy in 29 (15 with adjuvant chemotherapy), and biopsies only in 1 (with chemotherapy). Staging was possible in 56 tumors; according to the "uterine sarcoma" system (tumor size and extent) they were: stage I (10/56; could not be further subclassified as size not available), IA (22/56), IB (18/56), IIA (2/56), IIB 3/56), IIIC (1/56). According to the "adenosarcoma" system (depth of invasion and extent) they were: stage IA (26/56), IB (14/56), IC (10/56), IIA (2/56), IIB (3/56), IIIC (1/56). Eight patients had local recurrence following incomplete excision (10%). Eleven of 79 patients had extrauterine recurrences (14%) and 9 died of disease (11%). Older age was associated with extrauterine recurrence (median 44 vs. 22; P=0.002) and decreased disease-specific survival (median 44 vs. 22; P=0.02). For patients with tumors initially confined to the cervix, the adenosarcoma staging system was superior to the uterine sarcoma staging system for predicting survival (P=0.02). Three patients with DICER1 syndrome who underwent fertility-preserving surgery developed a second primary cERMS 7, 7, and 12 years after their primary tumor. All 9 patients with DICER1 syndrome had tumors confined to the cervix and none died of disease. This study highlights the intriguing clinical aspects of cERMS including its long-known tendency to occur in the young but also more recently appreciated association with DICER1 syndrome. Establishing the diagnosis may still be difficult because of the hazard of sampling a neoplasm which in areas may appear remarkably bland and also because of its potential confusion with other neoplasms. This study indicates that this tumor has a good prognosis at this site and in selected cases a conservative surgical approach is a realistic consideration.

The Small Round Cell Sarcomas Complexities and Desmoplastic Presentation

Background

Small round cell sarcomas (SRCSs) account for most solid malignancies in the pediatric age group and are a part of group of malignant tumors characterized by heterogenous clinical presentation and overlapping microscopic features of small, round, primitive cells. In addition to the recently established certain genetically defined subset of undifferentiated round cell sarcomas of soft tissue and bone, this group of sarcomas include desmoplastic small round cell tumor, poorly differentiated synovial sarcoma, alveolar rhabdomyosarcoma, mesenchymal chondrosarcoma, and small cell osteosarcoma. Although, those entities share clinical and cytomorphologic features and cannot be unequivocally classified based on clinical presentation and morphology alone. Most of SRCSs characterizes of particular patterns of protein expression or genetic changes and ancillary tests remain necessary to confirm or rule out a specific diagnosis. Subtle but occasionally distinctive cytologic features narrows the number of differential diagnoses and helps to select appropriate ancillary tests necessary for the final diagnosis. Thus, when adequate fine needle aspiration (FNA) biopsy specimen is combined with ancillary tests, a specific histologic diagnosis can be made in almost all cases. However, due to complex cytologic features of SRCS as well as various quality and diversity of FNA smears, there are cases in that cytologic features which do not entirely match the known diagnostic criteria.

Summary

The aim of this review was to summarize cytomorphologic criteria and to present rare and divergent cytological features of SRCSs. Careful assessment of clinical presentation, cytological features, immunohistochemical patterns, and molecular alternations is necessary for an accurate diagnosis. Knowing of rare and divergent microscopic findings that does not fit with the known cytological criteria will help to avoid misdiagnosis.

Key Messages

The role of FNA biopsies diagnosing soft tissue and bone tumors has been increasing because of the ability of ancillary tests to assist in the diagnosis of specific tumors. SRCSs may be diagnosed accurately in cytology specimens. Access to clinical and radiographic presentation, utility of ancillary tests, understanding complexity of cytological features, and awareness of the rare cytologic findings that differ from that of the established diagnostic criteria are essential to make correct diagnosis.

SIX1 reprograms myogenic transcription factors to maintain the rhabdomyosarcoma undifferentiated state

Rhabdomyosarcoma (RMS) is a pediatric muscle sarcoma characterized by expression of the myogenic lineage transcription factors (TFs) MYOD1 and MYOG. Despite high expression of these TFs, RMS cells fail to terminally differentiate, suggesting the presence of factors that alter their functions. Here, we demonstrate that the developmental TF SIX1 is highly expressed in RMS and critical for maintaining a muscle progenitor-like state. SIX1 loss induces differentiation of RMS cells into myotube-like cells and impedes tumor growth in vivo. We show that SIX1 maintains the RMS undifferentiated state by controlling enhancer activity and MYOD1 occupancy at loci more permissive to tumor growth over muscle differentiation. Finally, we demonstrate that a gene signature derived from SIX1 loss correlates with differentiation status and predicts RMS progression in human disease. Our findings demonstrate a master regulatory role of SIX1 in repression of RMS differentiation via genome-wide alterations in MYOD1 and MYOG-mediated transcription.

An Integrative Morphologic and Molecular Approach for Diagnosis of Rhabdomyosarcoma and Subclassification of Rhabdomyosarcoma

CONTEXT.—

Rhabdomyosarcoma, the most common soft tissue sarcoma of children, is currently classified into the following 4 subtypes: embryonal rhabdomyosarcoma, alveolar rhabdomyosarcoma, spindle cell/sclerosing rhabdomyosarcoma, and pleomorphic rhabdomyosarcoma, based on recent molecular genetic knowledge and morphologic features.

OBJECTIVE.—

To highlight the most recent advances of molecular genetic alterations, and to familiarize pathologists with most recent genotype and phenotype correlation in rhabdomyosarcoma.

DATA SOURCES.—

Data were derived from the World Health Organization Classification of Soft Tissue and Bone Tumors, fifth edition, recently published literature (PubMed), and clinical practice experience.

CONCLUSIONS.—

Current classification has been significantly impacted by genotype and phenotype correlation, especially with PAX-FOXO1 fusion-positive rhabdomyosarcoma versus fusion-negative rhabdomyosarcoma, and with emergence of 3 distinct new subtypes of spindle cell/sclerosing rhabdomyosarcoma. Although all rhabdomyosarcomas were considered to be a single diagnostic entity in the past, they are now considered to be a group of histologically similar but biologically diverse entities because their clinical behavior and underlying molecular alterations dramatically differ. This review outlines recent molecular genetic developments, corresponding morphologic features, and current challenges faced by pathologists in daily practice.

Primary Cutaneous Alveolar Rhabdomyosarcoma in an Elderly Adult: A Rare Potential Mimic of Merkel Cell Carcinoma

ABSTRACT

Rhabdomyosarcoma (RMS) rarely arises as a primary skin tumor. It is also very rare in older adults, especially the alveolar type. We report an 80-year-old White woman who presented with a painful, erythematous, raised lesion (2 × 3.5 cm) above the left knee that was fixed within the skin, yet mobile about underlying soft tissue. A punch biopsy showed monotonous malignant round blue cells involving the dermis. Immunostains showed diffuse expression of CD56, focal chromogranin, focal dot-like pancytokeratin, CK7, and neurofilament, but negative for synaptophysin, CK20, SOX-10, MUM-1, CD43, TTF-1, and CD99. A CK20-negative variant of Merkel cell carcinoma was initially favored, but given the unusual immunophenotype and the presence of cellular dyscohesion, desmin and myogenin stains were performed, both of which were diffusely positive. Molecular testing revealed rearrangement of PAX3 and FOXO1 loci, confirming the diagnosis of alveolar RMS. PET/CT showed a probable 1.9-cm left inguinal lymph node metastasis; no internal or deep soft tissue primary tumor mass was identified, supporting a true primary cutaneous origin. Alveolar RMS may express keratins and neuroendocrine markers, making it easy to confuse with Merkel cell carcinoma on those exceptionally rare instances, when it arises in the skin of older adults.

Population-Based Survival Analysis of Patients With Limb Rhabdomyosarcoma and Metastasis at Diagnosis

Purpose: Given the poor prognosis and the relative rarity of patients diagnosed with limb rhabdomyosarcoma (LRMS) and metastasis at diagnosis, we performed this study to reveal distinctive clinical features and evaluated prognostic factors of this special population in order to provide appropriate treatment.

Patients and Methods: We carried out retrospective research of patients diagnosed with LRMS and metastasis from 1975 to 2016 using the Surveillance, Epidemiology, and End Results (SEER) program database. Survival curves were generated by applying the Kaplan–Meier method. In terms of evaluating and determining independent predictors of survival, we conducted univariate and multivariate survival analyses using the Cox proportional hazard regression model.

Results: This retrospective analysis contained a series of 245 patients with metastatic LRMS, with male predominance (male vs. female, 1.6:1). Nearly half of the patients were diagnosed with alveolar rhabdomyosarcoma (44.9%). According to the results of the univariate and multivariate analyses, younger age, tumor subtype, and radiotherapy were found to be significantly associated with improved overall survival (OS) and cause-specific survival (CSS).

Conclusions: Patients with LRMS and metastasis at diagnosis experienced a quite poor prognosis. Age at diagnosis, tumor subtype, and radiotherapy can help clinicians to better estimate the prognosis. This study indicated that local radiotherapy can provide a survival benefit.

"Inflammatory Leiomyosarcoma" and "Histiocyte-rich Rhabdomyoblastic Tumor": a clinicopathological, immunohistochemical and genetic study of 13 cases, with a proposal for reclassification as "Inflammatory Rhabdomyoblastic Tumor"

Inflammatory leiomyosarcoma (ILMS), defined as "a malignant neoplasm showing smooth muscle differentiation, a prominent inflammatory infiltrate, and near-haploidization", is a very rare soft tissue tumor with a generally favorable prognosis. The morphologic features of "histiocyte-rich rhabdomyoblastic tumor" (HRRMT) are similar to those of ILMS, although this lesion shows by definition a skeletal muscle phenotype. Recent gene expression profiling and immunohistochemical studies have also suggested that ILMS and HRRMT may be related. We studied the clinicopathologic, immunohistochemical and genetic features of four cases previously classified as ILMS and nine classified as HRRMT. Tumors from both groups tended to occur in the deep soft tissues of the extremities of young to middle-aged males and exhibited indolent behavior. Morphologically, all were well-circumscribed, often encapsulated, and showed a striking histiocyte-rich inflammatory infiltrate admixed with variably pleomorphic tumor cells showing spindled and epithelioid to rhabdoid morphology, eosinophilic cytoplasm, and prominent nucleoli, but few, if any, mitotic figures. Immunohistochemically, the tumor cells expressed desmin, alpha-smooth muscle actin, and the rhabdomyoblastic markers PAX7, MyoD1, and myogenin. H-caldesmon expression was absent in all cases, using the specific h-CD antibody. Karyotypic study (1 HRRMT) and genome-wide copy number analysis (7 HRRMT, OncoScan SNP assay), revealed near-haploidization in four cases, with subsequent genome doubling in one, an identical phenotype to that seen in ILMS. We propose reclassification of ILMS and HRRMT as "inflammatory rhabdomyoblastic tumor", a name which accurately describes the salient morphologic and immunohistochemical features of this distinctive tumor, as well as its intermediate (rarely metastasizing) clinical behavior.

FOXF1 is required for the oncogenic properties of PAX3-FOXO1 in rhabdomyosarcoma

The PAX3-FOXO1 fusion protein is the key oncogenic driver in fusion positive rhabdomyosarcoma (FP-RMS), an aggressive soft tissue malignancy with a particularly poor prognosis. Identifying key downstream targets of PAX3-FOXO1 will provide new therapeutic opportunities for treatment of FP-RMS. Herein, we demonstrate that Forkhead Box F1 (FOXF1) transcription factor is uniquely expressed in FP-RMS and is required for FP-RMS tumorigenesis. The PAX3-FOXO1 directly binds to FOXF1 enhancers and induces FOXF1 gene expression. CRISPR/Cas9 mediated inactivation of either FOXF1 coding sequence or FOXF1 enhancers suppresses FP-RMS tumorigenesis even in the presence of PAX3-FOXO1 oncogene. Knockdown or genetic knockout of FOXF1 induces myogenic differentiation in PAX3-FOXO1-positive FP-RMS. Over-expression of FOXF1 decreases myogenic differentiation in primary human myoblasts. In FP-RMS tumor cells, FOXF1 protein binds chromatin near enhancers associated with FP-RMS gene signature. FOXF1 cooperates with PAX3-FOXO1 and E-box transcription factors MYOD1 and MYOG to regulate FP-RMS-specific gene expression. Altogether, FOXF1 functions downstream of PAX3-FOXO1 to promote FP-RMS tumorigenesis.

Rare Variant of Adult Rhabdomyosarcoma Presenting as a Palatal Swelling

A 26-year-old male was referred to the Department of Oral and Maxillofacial Surgery of a tertiary care hospital in Lahore with chief complaint of painless swelling on the right palate of 40 days duration. Clinical differential diagnosis included squamous cell carcinoma, Ewing sarcoma, fibrosarcoma, neuroblastoma and rhabdomyosarcoma. Computed tomography scan revealed hypodense mass with necrotic changes. Histological examination of the excised tumor revealed malignant neoplasm arranged in fascicles and bundles comprising of spindle cells with pleomorphic, hyperchromatic nuclei and increased atypical mitosis. Immunohistochemical analysis showed negative staining with Cytokeratin, S100, CD34, Stat6, h-Caldesmon and EMA while the tumour cells were positive for desmin, myogenin, smooth muscle actin, CD-99 and MyoD1 thus confirming the diagnosis of spindle cell rhabdomyosarcoma.

Embryonal Rhabdomyosarcoma Presenting as Lung Metastasis in an Adult: An Uncommon Presentation

Rhabdomyosarcoma (RMS) is one of the most common soft tissue sarcomas of adolescents and young adults. Histologically, rhabdomyosarcoma is classified into embryonal, alveolar, pleomorphic, and spindle cell/sclerosing rhabdomyosarcomas with further subcategorization. More than 50% of embryonal rhabdomyosarcoma occur within head and neck. The retroperitoneum and pelvis are less common sites of involvement. Embryonal rhabdomyosarcomas affect mainly, but not exclusively, children between birth and 15 years of age. Alveolar rhabdomyosarcoma tends to affect older patients. The usual metastatic sites include lung, lymph nodes, and bone marrow. We are presenting a case of a 25-year-old male patient with symptoms of breathlessness, easy fatigability, and weight loss. On chest imaging, there were multiple lung nodules. A primary diagnosis of undifferentiated malignant neoplasm was made on lung biopsy. On immunohistochemistry, the malignant cells were positive for myogenin, myoblast determination protein 1 (MyoD1), and desmin. They were negative for neuroendocrine, germ cell, epithelial, melanocytic, and lymphoid markers. Further workup showed an abdominopelvic retroperitoneal mass on abdominal computed tomography (CT) scan. The biopsy on the retroperitoneal mass showed similar morphology and immunohistochemical profile. Unfortunately, the patient's condition deteriorated rapidly in the following weeks, and he passed away.

Alveolar rhabdomyosarcomas involving serous cavity fluid specimens exhibit diverse cytomorphologies: A case report and review of the literature

Involvement of serous cavity specimens by alveolar rhabdomyosarcoma (ARMS) is a rare event and only a few case reports have been reported in the literature, with conflicting cytomorphologic patterns. Herein, we report on a 41-year-old man with no significant past medical history who presented with pancytopenia and shortness of breath and was found to have widely metastatic sinonasal alveolar rhabdomyosarcoma, including involvement of the pleura. The pleural fluid specimen was cellular and contained ARMS cells in small-to-medium sized three-dimensional fragments that resembled an adenocarcinoma or mesothelioma, and numerous single cells were seen in the background. The individual tumor cells demonstrated variable morphology; all were large, with varying degree of cytoplasm, and multinucleated cells were commonly seen in the background. The cells were negative for calretinin and claudin-4 and were positive for myogenin, confirming the diagnosis. Given the cytomorphologic diversity of ARMS seen in serous fluid specimens, patient history and the use of confirmatory immunostains are essential.

MiR-7 mediates mitochondrial impairment to trigger apoptosis and necroptosis in Rhabdomyosarcoma

BACKGROUND

Rhabdomyosarcoma (RMS) is a pediatric cancer with rhabdomyoblastic phenotype and mitochondria act as pivotal regulators of its growth and progression. While miR-7-5p (miR-7) is reported to have a tumor-suppressive role, little is yet known about its antitumor activity in RMS.

METHODS

The effects of miR-7 on RMS were analyzed both in vitro and in vivo. Cell death modalities induced by miR-7 were identified. Influence on mitochondria was evaluated through RNA sequencing data, morphological observation and mitochondrial functional assays, including outer membrane permeability, bioenergetics and redox balance. Dual-luciferase assay and phenotype validation after transient gene silencing were performed to identify miR-7 targets in RMS.

RESULTS

MiR-7 executed anti-tumor effect in RMS beyond proliferation inhibition. Morphologic features and molecular characteristics with apoptosis and necroptosis were found in miR-7-transfected RMS cells. Chemical inhibitors of apoptosis and necroptosis were able to prevent miR-7-induced cell death. Further, we identified that mitochondrial impairment mainly contributed to these phenomena and mitochondrial proteins SLC25A37 and TIMM50 were crucial targets for miR-7 to induce cell death in RMS.

CONCLUSION

Our results extended the mechanism of miR-7 antitumor role in rhabdomyosarcoma cancer, and provided potential implications for its therapy.

Nek9,a sensitive immunohistochemical marker for Schwannian, melanocytic and myogenic tumours

AIMS

In our previous study, striking Nek9 staining was observed in peripheral nerves for the first time. Therefore, in the current study, we aimed to detect Nek9 expression in peripheral nerve sheath tumours, melanocytic tumours and their mimics.

METHODS

The expression of Nek9 was analysed in 234 mesenchymal tumours including schwannoma, neurofibroma, malignant peripheral nerve sheath tumour (MPNST), melanoma and their mimics adopting immunohistochemistry. In addition, S-100 and SOX10 were detected in all tumours.

RESULTS

The results revealed an intense and diffuse staining of Nek9 in all schwannomas (30/30) and melanomas (20/20). The neurofibromas (86%, 19/22) and MPNSTs (76%, 18/21) showed a high frequency of positive Nek9 staining. Nek9 showed a comparable sensitivity to S-100, and better sensitivity and less specificity than that of SOX10. Among the histological mimics, Nek9 was only strongly and diffusely expressed in rhabdomyosarcomas (RSs) (97%,37/38) while negatively stained in most of the other tumours. It was noted that Nek9 immunoresponse was more diffuse than that of MyoD1 and myogenin in RS.

CONCLUSIONS

In summary, Nek9 has a good sensitivity in the diagnosis of tumours with Schwannian, melanocytic and skeletal muscle differentiations. The immunohistochemical analysis of Nek9 expression may be helpful in the diagnosis and differential diagnosis of the aforementioned tumours.

[Sclerosing rhabdomyosarcoma of the parotid gland: Unusual location of a rare mesenchymal tumor]

Rhabdomyosarcoma is a malignant mesenchymal tumour with skeletal muscle differentiation. Its sclerosing variant is a rare entity, which is described in the latest WHO edition of soft tissues in association with the spindle cell subtype, with which it shares clinical, morphological and cytogenetic features. Cytogenetic advances have allowed a prognostic approach to fusiform/sclerosing cell rhabdomyosarcoma by individualizing 3 different genomic prognostic groups. The parotid location of sclerosing rhabdomyosarcoma is exceptional with only two reported cases in the literature. It can pose a diagnostic challenge because of its rarity and histological similarities with other malignancies. We report the third case of sclerosing rhabdomyosarcoma of the parotid gland, which occurred in a 7-year old girl, who had consulted for a painless swelling of the parotid region of 4 months duration. Gross examination of the partial parotidectomy demonstrated an ill-circumscribed 35×30mm, firm and white glistening tumor. Histologically, it was composed of cords and trabeculae of small round cells, with ovoid and often irregular nuclei. Mitoses were numerous. The cytoplasm was scanty and cell margins were unclear. Tumor cells were set in a prominent hyalinized matrix. Scattered rhabdomyoblastic-like tumor cells were noted. The diagnosis of sclerosing rhabdomyosarcoma was performed after the positive immunostaining with desmin, myogenin and smooth muscle actin. No cytogenetic or molecular studies were performed. The patient underwent adjuvant chemo and radiotherapy, without recurrences or distant metastases during the 8-year follow-up.

MRI of Rhabdomyosarcoma and Other Soft-Tissue Sarcomas in Children

Soft-tissue sarcomas in children comprise a heterogeneous group of entities with variable manifestation depending on the age of the patient and the location of the tumor. MRI is the modality of choice for evaluating musculoskeletal soft-tissue tumors and plays a paramount role in both initial diagnosis and assessment of tumor response during and after treatment. Conventional MRI sequences, such as T1- and T2-weighted imaging, offer morphologic information, which is important for localizing the lesion and describing anatomic relationships but not accurate for determining its malignant or benign nature and may be limited in differentiating tumor response from therapy-related changes. Advanced multiparametric MRI offers further functional information that can help with these tasks by using different imaging sequences and biomarkers. The authors present the role of MRI in rhabdomyosarcoma and other soft-tissue sarcomas in children, emphasizing a multiparametric approach with focus on the utility and potential added value of diffusion-weighted imaging (DWI) and dynamic contrast-enhanced MRI in characterization and staging, determination of pretreatment extent, and evaluation of tumor response and recurrence after treatment. ^©RSNA, 2020.

The current landscape of rhabdomyosarcomas: an update

Rhabdomyosarcomas are malignancies associated with a rhabdomyoblastic phenotype which can be demonstrated morphologically or by immunohistochemistry for MYOD1 and myogenin. Rhabdomyosarcomas are currently subdivided into 4 types in the 2013 WHO classification of tumors of soft tissue and bone, including embryonal rhabdomyosarcoma, alveolar rhabdomyosarcoma, spindle cell/sclerosing rhabdomyosarcoma, and pleomorphic rhabdomyosarcoma. Recent studies have significantly impacted this classification with the emergence of three distinct new subtypes of rhabdomyosarcomas, namely rhabdomyosarcoma with MYOD1 mutations, rhabdomyosarcoma with TFCP2 fusions, and rhabdomyosarcoma with VGLL2/NCOA2 fusions. Although all these tumors share the terminology "rhabdomyosarcoma," their morphology, clinical behavior, and underlying molecular alterations are dramatically different. Finally, the presence of a rhabdomyoblastic phenotype within a tumor is by no means a diagnostic of a rhabdomyosarcoma, as this may be seen in many other mesenchymal malignancies, such as mesenchymal chondrosarcomas, malignant peripheral nerve sheaths tumors, and biphenotypic sinonasal sarcomas. In this review, we present the main clinical, morphological, and molecular features of these tumors and discuss the evolution of the current classification.