Evolving classification of rhabdomyosarcoma

Rhabdomyosarcomas comprise the single largest category of soft tissue sarcomas in children and adolescents in the United States, occurring in 4.5 million people aged below 20 years. Based on the clinicopathological features and genetic abnormalities identified, rhabdomyosarcomas are classified into embryonal, alveolar, spindle cell/sclerosing and pleomorphic subtypes. Each subtype shows distinctive morphology and has characteristic genetic abnormalities. This review discusses the evolution of the classification of rhabdomyosarcoma to the present day, together with a discussion of key histomorphological and genetic features of each subtype and the diagnostic approach to these tumours.

Molecular Alterations in Pediatric Fibroblastic/Myofibroblastic Tumors: An Appraisal of a Next Generation Sequencing Assay in a Retrospective Single Centre Study

BACKGROUND

Pediatric fibroblastic/myofibroblastic tumors (PFMTs) can be challenging to definitively classify. Large case series or diagnostic updates have not been recently published despite identification of molecular alterations that could improve diagnostic accuracy. Our review of the literature found that over two-thirds of the more than 30 types of PFMTs harbor recurrent molecular alterations. We performed an institutional review of PFMTs to highlight limitations of a predominantly morphological classification, and evaluated the utility of a next-generation sequencing assay to aid diagnosis.

METHODS

PFMTs identified over a period of 12 years were reviewed, categorized per the new WHO classification, and tested using the Oncomine Childhood Cancer Research Assay.

RESULTS

Eighty-seven specimens from 58 patients were reviewed; 50 were chosen for molecular analysis, 16 (32%) lacking definitive classification. We identified alterations, some novel, in 33% of assayed cases. Expected alterations were identified for most known diagnoses and mutations were identified in 6 of 16 tumors (38%) that were initially unclassified.

CONCLUSION

We confirmed a significant subset of PFMTs remain difficult to classify using current criteria, and that a combined DNA/RNA assay can identify alterations in many of these cases, improving diagnostic certainty and suggesting a clinical utility for challenging cases.

DNA methylation-based profiling of bone and soft tissue tumours: a validation study of the 'DKFZ Sarcoma Classifier'

Diagnosing bone and soft tissue neoplasms remains challenging because of the large number of subtypes, many of which lack diagnostic biomarkers. DNA methylation profiles have proven to be a reliable basis for the classification of brain tumours and, following this success, a DNA methylation-based sarcoma classification tool from the Deutsches Krebsforschungszentrum (DKFZ) in Heidelberg has been developed. In this study, we assessed the performance of their classifier on DNA methylation profiles of an independent data set of 986 bone and soft tissue tumours and controls. We found that the 'DKFZ Sarcoma Classifier' was able to produce a diagnostic prediction for 55% of the 986 samples, with 83% of these predictions concordant with the histological diagnosis. On limiting the validation to the 820 cases with histological diagnoses for which the DKFZ Classifier was trained, 61% of cases received a prediction, and the histological diagnosis was concordant with the predicted methylation class in 88% of these cases, findings comparable to those reported in the DKFZ Classifier paper. The classifier performed best when diagnosing mesenchymal chondrosarcomas (CHSs, 88% sensitivity), chordomas (85% sensitivity), and fibrous dysplasia (83% sensitivity). Amongst the subtypes least often classified correctly were clear cell CHSs (14% sensitivity), malignant peripheral nerve sheath tumours (27% sensitivity), and pleomorphic liposarcomas (29% sensitivity). The classifier predictions resulted in revision of the histological diagnosis in six of our cases. We observed that, although a higher tumour purity resulted in a greater likelihood of a prediction being made, it did not correlate with classifier accuracy. Our results show that the DKFZ Classifier represents a powerful research tool for exploring the pathogenesis of sarcoma; with refinement, it has the potential to be a valuable diagnostic tool.

DNA methylation patterns-based subtype distinction and identification of soft tissue sarcoma prognosis

Soft tissue sarcomas (STSs) are heterogeneous at the clinical with a variable tendency of aggressive behavior. In this study, we constructed a specific DNA methylation-based classification to identify the distinct prognosis-subtypes of STSs based on the DNA methylation spectrum from the TCGA database. Eventually, samples were clustered into 4 subgroups, and their survival curves were distinct from each other. Meanwhile, the samples in each subgroup reflected differentially in several clinical features. Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis was also conducted on the genes of the corresponding promoter regions of the above-described specific methylation sites, revealing that these genes were mainly concentrated in certain cancer-associated biological functions and pathways. In addition, we calculated the differences among clustered methylation sites and performed the specific methylation sites with LASSO algorithm. The selection operator algorithm was employed to derive a risk signature model, and a prognostic signature based on these methylation sites performed well for risk stratification in STSs patients. At last, a nomogram consisted of clinical features and risk score was developed for the survival prediction. This study declares that DNA methylation-based STSs subtype classification is highly relevant for future development of personalized therapy as it identifies the prediction value of patient prognosis.

The 2020 WHO Classification of Tumors of Soft Tissue: Selected Changes and New Entities

Soft tissue tumors are a relatively rare and diagnostically challenging group of neoplasms that can have varying lines of differentiation. Accurate diagnosis is important for appropriate treatment and prognostication. In the 8 years since the publication of the 4th Edition of World Health Organization (WHO) classification of soft tissue tumors, significant advances have been made in our understanding of soft tissue tumor molecular biology and diagnostic criteria. The 5th Edition of the 2020 WHO classification of tumors of soft tissue and bone incorporated these changes. Classification of tumors, in general, but particularly in soft tissue tumors, is increasingly based on the molecular characteristics of tumor types. Understanding tumor molecular genetics improves diagnostic accuracy for tumors that have been difficult to classify on the basis of morphology alone, or that have overlapping morphologic features. In many large hospitals in the United States and Europe, molecular tests on soft tissue tumors are a routine part of diagnosis. Therefore, surgical pathologists should be familiar with newly emerging molecular genetic techniques in clinical settings. In the near future, molecular tests, particularly in soft tissue tumor diagnosis, will become as routine during diagnosis as immunohistochemistry is currently. This new edition provides an updated classification scheme and essential diagnostic criteria for soft tissue tumors. Newly recognized entities and subtypes of existing tumor types, several reclassified tumors, and newly defined molecular and genetic data have been incorporated. Herein, we summarize the updates in the WHO 5th Edition, focusing on major changes in each category of soft tissue tumor, and the newly described tumor entities and subtypes.

Novel Aspects of Genetics, Molecular Biology and Clinical Oncology of Sarcomas

The Connective Tissue Oncology Group Annual Meeting 2018 (CTOS 2018) took place in Rome from 4 to 17 November 2018, and the 39th Plenary Meeting of the Scandinavian Sarcoma Group (SSGM 2019) was held in Bergen from 8 to 10 May 2019. These two large international conferences brought together an overwhelming majority of molecular and clinical specialists in the sarcoma field, especially those working on soft tissue sarcoma. Topics discussed on the conferences included, among others, sarcoma genetics, clinical and molecular subclassification, targeted therapy, clinical prognostication, and new experimental sarcoma models. A large ongoing international study on germinal sarcoma genetics was presented, the interim results of which revealed the extremely complex nature of genetic disposition to sarcoma, and, surprisingly, a rather prominent place among predisposing genes for those coding for structural telomere constituents. Fusion oncogenes dominate somatic sarcoma genetics, especially because of their origin and impact on sarcoma clinical behaviour, and are especially relevant for karyotypically simple paediatric sarcomas. A crucial issue in karyotypically complex sarcomas are the efforts being made to obtain a subclassification of sarcoma, other than those based on pathology, using either the clinical characteristics of sarcomas (uterine leiomyosarcoma vs. soft tissue leiomyosarcoma) or specific gene expression profiles (molecular subtypes in undifferentiated pleiomorphic sarcoma), which showed that molecular characterization can open the way for subtype specific therapies. Other examples of where this type of strategy can be applied include gastrointestinal stromal tumours, infantile fibrosarcoma, and inflammatory myofibroblastic tumours, where targeted therapy could be conceived based on the actionable mutations identified. Attempts in this direction have been made also for clear cell sarcoma and dedifferentiated liposarcoma, albeit the effectiveness of molecular-targeted treatments for these sarcomas is still poor, and progress in the treatment of osteosarcoma is still rather slow. Actually, the platelet-derived growth factor signalling system holds a prominent position in searches for targeted therapies, not only against rare sarcoma types, where are activated by mutations (some gastrointestinal stromal tumours, infantile hereditary myofibromatosis, and dermatofibrosarcoma protuberans), but also against other more usual sarcoma types, where the blocking anti-PDGFRα-antibody olaratumab has been successfully integrated into combinatorial chemotherapeutic regimens. In the field of clinical prognostication, remarkable progress in sarcoma nomograms was reported. Interesting results were also presented in the area of new experimental sarcoma models. Participation on both scientifi c conferences and all the experimental work leading to the presented sarcoma models were supported by the Czech Science Foundation project No. 17-17636S. The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers. Submitted: 20. 9. 2019 Accepted: 6. 11. 2019.

Mesenchymal Tumors with EWSR1 Gene Rearrangements

Among the various genes that can be rearranged in soft tissue neoplasms associated with nonrandom chromosomal translocations, EWSR1 is the most frequent one to partner with other genes to generate recurrent fusion genes. This leads to a spectrum of clinically and pathologically diverse mesenchymal and nonmesenchymal neoplasms, variably manifesting as small round cell, spindle cell, clear cell or adipocytic tumors, or tumors with distinctive myxoid stroma. This review summarizes the growing list of mesenchymal neoplasms that are associated with EWSR1 gene rearrangements.

PRDM10-rearranged Soft Tissue Tumor: A Clinicopathologic Study of 9 Cases

Gene fusion transcripts containing PRDM10 were recently identified in low-grade undifferentiated pleomorphic sarcomas (UPS). Here, we describe the morphologic and clinical features of 9 such tumors from 5 men and 4 women (age: 20 to 61 y). Three cases had previously been diagnosed as UPS, 3 as superficial CD34-positive fibroblastic tumor (SCD34FT), 2 as pleomorphic liposarcoma, and 1 as pleomorphic hyalinizing angiectatic tumor. The tumors were located in the superficial and deep soft tissues of the thigh/knee region (4 cases), shoulder (2 cases), foot, trunk, and perineum (1 case each) ranging in size from 1 to 6 cm. All showed poorly defined cellular fascicles of pleomorphic cells within a fibrous stroma with frequent myxoid change and a prominent inflammatory infiltrate. All displayed highly pleomorphic nuclear features, but a low mitotic count. Most tumors were well circumscribed. One of 9 tumors recurred locally, but none metastasized. Immunohistochemically, all were CD34 and showed nuclear positivity for PRDM10; focal positivity for cytokeratins was seen in 5/6 cases. PRDM10 immunoreactivity was evaluated in 50 soft tissue tumors that could mimic PRDM10-rearranged tumors, including 4 cases exhibiting histologic features within the spectrum of SCD34FT. Except for 2/6 pleomorphic liposarcomas and 1/4 myxofibrosarcomas, other tumors did not show nuclear positivity but displayed weak to moderate cytoplasmic immunoreactivity. In conclusion, PRDM10-rearranged soft tissue tumor is characterized by pleomorphic morphology and a low mitotic count. Its morphologic spectrum overlaps with SCD34FT. Clinical features of this small series suggest an indolent behavior, justifying its distinction from UPS and other sarcomas.

Important Recently Characterized Non-Ewing Small Round Cell Tumors

Round cell sarcomas morphologically similar to Ewing sarcoma, but lacking the classic immunohistochemical features, EWSR-ETS family fusions, and other signs of differentiation, are classified as Ewing-like sarcomas. Recent molecular advances led to the discovery and characterization of two recurrent oncogenic fusion rearrangements, CIC-DUX4 and BCOR-CCNB3, in a significant subset of Ewing-like sarcomas. Uncovered alternate fusion partners broadened the proposed classification of these tumors to CIC-rearranged sarcomas and BCOR-rearranged sarcomas. This article summarizes the clinicopathologic and molecular features of these entities, with particular attention paid to those features that overlap with and distinguish these sarcomas from other round cell sarcomas.

Pleomorphic Sarcomas: The State of the Art

This article focuses on pleomorphic sarcomas, which are malignant mesenchymal tumors with complex genetic background at the root of their morphologic pleomorphism. They are poorly differentiated tumors that may retain different lines of differentiation, sometimes correlating with clinicopathological or prognostic features. Accurate diagnosis in this group of tumors relies on adequate sampling due to their heterogeneity and assessment with both microscopy and large panels of immunohistochemistry. Molecular analyses have a limited role in their diagnosis as opposed to translocation-related sarcomas but may provide theranostic and important prognostic information in the future.

Advances in the Genetic Characterization of Cutaneous Mesenchymal Neoplasms: Implications for Tumor Classification and Novel Diagnostic Markers

Cutaneous mesenchymal neoplasms often pose significant diagnostic challenges; many such entities are rare or show clinical and histologic overlap with both other mesenchymal and non-mesenchymal lesions. Recent advances in the genetic classification of many cutaneous mesenchymal neoplasms have not only helped define unique pathologic entities and increase our understanding of their biology, but have also provided new diagnostic markers. This review details these recent discoveries, with a focus on their implications for tumor classification and diagnosis.

Morphologic Spectrum of Desmoid-Type Fibromatosis

OBJECTIVES

Desmoid-type fibromatosis is a locally aggressive neoplasm composed of long sweeping fascicles of bland fibroblasts/myofibroblasts. Tumors with classic features are easy to identify, but the morphologic spectrum of this entity spans beyond the conventional histologic pattern. Since sampling of an unrecognized histologic variant may lead to misdiagnosis, especially on small needle biopsy specimens, we sought to fully characterize the morphologic spectrum of this entity.

METHODS

We examined 165 cases of desmoid-type fibromatosis and catalogued the morphologic patterns and percentage of those patterns identified in each case. Clinicopathologic variables, including age, sex, location, and recurrence, were analyzed and correlated with pattern frequency.

RESULTS

Seven morphologic patterns were identified, including conventional, hyalinized/hypocellular, staghorn vessel, myxoid, keloidal, nodular fasciitis-like, and hypercellular. The mean number of patterns per case was two, but some cases harbored up to five patterns. The greatest morphologic variability was seen in the intra-abdominal lesions, with these tumors having a significantly higher percentage of the keloidal and staghorn patterns compared with extra-abdominal and abdominal wall sites. No significant correlation between patient outcome (recurrence) and presence of variant morphologic pattern was observed (P = .549).

CONCLUSIONS

The morphologic spectrum of desmoid-type fibromatosis is deceptively broad, and awareness of the variety of histologic patterns is critical for accurate diagnosis.

[WHO classification of tumours of soft tissue and bone 2013: the main changes compared to the 3rd edition]

In early 2013, the new classification of tumours of soft tissue and bones was released. This edition belongs to the fourth series of so-called Blue Books published under the auspices of the World Health Organisation (WHO). The current classification follows the previous third edition, from which it differs in several aspects. The vast majority of changes are related to the soft tissue tumour section, which was enriched with three new chapters, some entities or terms were removed, new diagnoses were introduced, and several tumours were reallocated to other categories. Albeit to a lesser extent, similar changes have occurred also in the classification of bone tumours. Compared to the previous edition, more detailed molecular and cytogenetic data were incorporated in the current issue. The rapidly increasing knowledge of the genetics of mesenchymal tumours allows us to make more accurate diagnoses as well as to better understand of the pathogenesis of these lesions. However, abundant molecular and cytogenetic data highlight an increasing problem of growing numbers of genetic overlaps even among quite different tumours. The coexistence of several grading systems of soft tissue tumours is another controversial issue mentioned in the recent WHO classification. The main advantages and limitations of the two most widely used grading systems are also discussed.

Soft tissue sarcomas--new approaches to diagnosis and classification

The study of sarcoma pathology is a rapidly evolving field. The continued refinement of classic diagnostic techniques in conjunction with the molecular diagnostics has resulted in an abundance of data regarding this diverse and rare group of tumors. We anticipate that cutting edge technology including next generation sequencing will continue to further our understanding of saromagenesis and enable more precise classification and diagnosis of sarcomas in the future.

The past, present, and future of cytotoxic chemotherapy and pathway-directed targeted agents for soft tissue sarcoma

The individual rarity of the many subtypes of soft tissue sarcomas has historically mandated an empiric approach to systemic therapy. Doxorubicin, first reported to have activity in sarcomas 40 years ago, remains the generalizable first-line treatment of choice for many subtypes, with no other drug or combination having shown an overall-survival advantage. Other cytotoxic agents, such as paclitaxel for angiosarcoma or gemcitabine with docetaxel for leiomyosarcoma, are commonly used for certain histologic subtypes based on relatively small studies. Trabectedin, particularly active against leiomyosarcoma and myxoid liposarcoma, is approved in many countries worldwide but not yet in the United States or Australia. Newer cytotoxic agents, including ifosfamide derivatives, are in current phase III testing. Although advances is systemic therapy of soft-tissue sarcomas have been hampered by their biologic heterogeneity, this diversity also serves as fertile ground for discovery and validation of targetable molecular drivers. The most notable success in this regard has been the development of small molecule therapies for gastrointestinal stromal tumors. Other targets of recent interest include mouse double minute 2 homolog (MDM2) in dedifferentiated liposarcoma and anaplastic lymphoma kinase (ALK) in inflammatory myofibroblastic tumor. Molecular therapies that have shown activity in diverse sarcoma populations include mammalian target of rapamycin (mTOR) inhibitors and vascular endothelial growth factor (VEGF-R) inhibitors. Among the latter, pazopanib demonstrated a progression-free survival over placebo in prior-treated patients with advanced sarcoma, and is now approved for use in the sarcomas in many countries. Efforts to understand the key molecular aberrations in any particular tumor continue towards a goal of individualized sarcoma therapy.

CLASSIFICATION OF BENIGN FATTY TUMOURS OF THE UPPER LIMB

In this paper, the authors offer a classification of benign fatty tumours of the upper limb. There are three histologically distinct types of fat cells: immature fat cells which give rise to lipoblastomas, mature brown fat cells which give rise to hibernomas and mature white fat cells which give rise to lipomas. Lipomas are the most common and they are sub-classified according to the anatomic site of fat cells into dermal, subcutaneous and sub-fascial lipomas; or tumours directly related to muscle, bone, synovium or nerve. Finally, the authors review 67 patients with benign fatty tumours of the upper limb and provide clinical examples of these tumours including their characteristic histological and radiological features.

In vivo 1H MRS for musculoskeletal lesion characterization: which factors affect diagnostic accuracy?

In vivo (1)H MRS is a noninvasive imaging technique for the identification of malignancy. Musculoskeletal lesions vary in their composition, causing field inhomogeneity and magnetic susceptibility effects which may be technical and diagnostic challenges for MRS. This study investigated the factors that affect diagnostic accuracy in the use of MRS for the characterization of musculoskeletal neoplasms. During a 7-year period, 210 consecutive patients with musculoskeletal lesions larger than 1.5 cm in diameter were examined. MRS of a single-voxel point-resolved spectroscopy sequence with TE = 135 ms was undertaken using a 1.5-T scanner. Lesions with a choline signal-to-noise ratio larger than 3.0 were considered to be malignant tumors. The diagnostic accuracy was calculated for all lesions and for subgroups on the basis of lesion type (bone and soft tissue), lesion composition (mixed and solid nonsclerotic), lesion size (≤4, >4-10 and >10 cm), MR scanner (MR scanner 1 and 2) and selected voxel size (≤3, >3-8 and >8 cm(3)). Multivariate logistic regressions were performed to estimate the associations between each factor and diagnostic accuracy. The diagnostic accuracy was 73.3% for all lesions. The accuracy was 54.4% for mixed lesions and 80.4% for solid nonsclerotic lesions (p < 0.001). The diagnostic accuracy was lower for larger lesions [86.8% for lesions of ≤4 cm, 71.6% for lesions of >4-10 cm (p = 0.04) and 63.6% for lesions of >10 cm (p = 0.007)]. There was no difference in diagnostic accuracy for bone versus soft-tissue lesions or as a function of MR scanner or voxel size. By the use of multivariate logistic regression, a solid nonsclerotic lesion was 3.15 times (95% confidence interval, 1.59-6.27) more likely than a mixed lesion to have a diagnosis (p = 0.001). MRS can be used to characterize musculoskeletal lesions, particularly solid nonsclerotic lesions.

Biology, classification, and management of recurrent myxofibrosarcoma 21 years after resection

Soft-tissue sarcomas (STSs) are a heterogenous group of rare malignancies that have significant lifelong implications. Accepted management options include limb-sparing surgical resection and adjuvant radiation therapy. Here we present the case of a myxoid malignant fibrous histiocytoma, now termed a myxofibrosarcoma, which recurred 21 years after primary surgical resection. To our knowledge, this is the longest documented interval between initial management and recurrence of an STS. Significant changes have been made in classification guidelines and diagnostic methods over this 2-decade period. The pathogenesis of remote recurrence of STSs remains controversial and is discussed in this report.

Principles of chest wall resection and reconstruction

Despite significant improvements in surgical technique and perioperative care, the management of patients requiring chest wall resection and reconstruction is an ongoing challenge for thoracic surgeons. A successful approach includes a thorough assessment of the patient and the lesion, an adequate biopsy to confirm tissue diagnosis, and a well-established treatment plan. In the case of a primary tumor of the chest wall, the extent of the resection should not be limited by the size of the resulting defect. Following resection, chest wall reconstruction mandates an appreciation for restoration of functional and structural components. An algorithmic approach to chest wall reconstruction begins with the assessment of the nature of the defect, taking into consideration factors such as infection, tumor location, previous radiation therapy, and surgical intervention. The latter factors bear influence on the type of tissue required as well as whether reconstruction can be performed in a single stage or whether it is better delayed. Finally, patient factors including lifestyle and work, as well as prognosis, are considered to determine the best reconstructive option.

The natural history and prognosticative factors of adult extremity soft tissue sarcomas: an Asian perspective

INTRODUCTION

We describe the natural history of Asian adult soft tissue sarcomas (STSs) in the extremities and predict prognosticative factors for local recurrence, metastasis and tumour-related death.

MATERIALS AND METHODS

Between January 1999 and May 2009, 67 adult patients with first presentation STSs of extremity sites underwent surgical treatment at a single institution. The associations between patient demographics and pathological features with local recurrence, metastasis and mortality were studied using univariate and multivariate analysis.

RESULTS

The mean age of our patients was 52.4 years with most presentations occurring in the thigh. Majority of Asian STSs were high grade (61.3%) and large tumours with 81.0% being >5 cm. Stages Ia, Ib, IIa, IIb, IIc, III and IV accounted for 6.6%, 6.6%, 26.2%, 11.5%, 3.3%, 42.6% and 3.3% of presentations, respectively. Patients were followed-up for a mean period of 45.9 months. On univariate analysis, high tumour grade and advanced stage (IIc to IV) were predictive of local recurrence and metastasis. Deep lesions were more likely to recur but not metastasise or cause death. Age, sex, size, and margin positivity were not predictive for all end-points. On multivariate testing, only pathological high grade was associated adversely with local recurrence [odds ratio (OR) = 10.0, 95% CI, 1.2 to 84.9, P = 0.035], metastasis (OR = 12.7, 95% CI, 2.46 to 65.2, P = 0.002) and mortality (OR = 16.2, 95% CI, 1.95 to 135.0, P = 0.010).

CONCLUSIONS

Asian adult extremity soft tissue sarcomas present late and are most commonly found in the thigh. High pathological grade is a consistent independent predictor for local failure, distant spread and tumour-related death. Our results reaffirm the current thinking that tumour biology is of primary importance in determining patient outcomes.

[Spindle cell rhabdomyosarcoma in adults: a new entity in the spectrum of malignant mesenchymal tumors of soft tissues]

Rhabdomyosarcomas (RMS) are rare soft tissue sarcomas showing a skeletal muscle differentiation. Histologically, embryonal, alveolar and pleomorphic subtypes are distinguished. RMS represent one of the most frequent sarcomas in children and adolescents, and in this age group embryonal and alveolar subtypes predominate. RMS in adults is extremely rare, and the pleomorphic subtype is most frequently seen. Spindle cell and sclerosing RMS in adults are very rare and, unlike the morphologically comparable tumors in children and adolescents, clinically aggressive neoplasms, which need to be distinguished from spindle cell malignant melanoma, spindle cell sarcomatoid carcinoma and from a number of spindle cell sarcomas of varying lines of differentiation. Spindle cell and sclerosing RMS in adults arise predominantly in the head and neck region and on the extremities, and are composed of atypical spindled cells and scattered rhabdomyoblasts. Since spindle cell RMS may contain areas of lower cellularity with abundant sclerosing stroma, and sclerosing RMS may show focal areas of increased cellularity, it is most likely that both forms represent a morphological spectrum of a single RMS variant.

Molecular classification of soft tissue sarcomas and its clinical applications

Sarcomas are a heterogeneous group of tumors that are traditionally classified according to the morphology and type of tissue that they resemble, such as rhabdomyosarcoma, which resembles skeletal muscle. However, the cell of origin is unclear in numerous sarcomas. Molecular genetics analyses have not only assisted in understanding the molecular mechanism in sarcoma pathogenesis but also demonstrated new relationships within different types of sarcomas leading to a more proper classification of sarcomas. Molecular classification based on the genetic alteration divides sarcomas into two main categories: (i) sarcomas with specific genetic alterations; which can further be subclassified based on a) reciprocal translocations resulting in oncogenic fusion transcripts (e.g. EWSR1-FLI1 in Ewing sarcoma) and b) specific oncogenic mutations (e.g. KIT and PDGFRA mutations in gastrointestinal stromal tumors) and (ii) sarcomas displaying multiple, complex karyotypic abnormalities with no specific pattern, including leiomyo-sarcoma, and pleomorphic liposarcoma. These specific genetic alterations are an important adjunct to standard morphological and immunohistochemical diagnoses, and in some cases have a prognostic value, e. g., Ewing family tumors, synovial sarcoma, and alveolar rhabdomyosarcoma. In addition, these studies may also serve as markers to detect minimal residual disease and can aid in staging or monitor the efficacy of therapy. Furthermore, sarcoma-specific fusion genes and other emerging molecular events may also represent potential targets for novel therapeutic approaches such as Gleevec for dermatofibrosarcoma protuberans. Therefore, increased understanding of the molecular biology of sarcomas is leading towards development of newer and more effective treatment regimens. The review focuses on recent advances in molecular genetic alterations having an impact on diagnostics, prognostication and clinical management of selected sarcomas.

[Classification of solid soft tissue tumours by ultrasonography]

PURPOSE

Malignant soft tissue tumours appear infrequently in comparison to benign lesions. Clinical misdiagnosis leads to inadequate or delayed therapy in many cases of soft tissue sarcoma. The present study explores the question if ultrasonography as a widely-used diagnostic tool allows for a discrimination of benign and malignant soft tissue tumours.

MATERIALS AND METHODS

In a prospective study over a period of 8 years 224 histologically ascertained solid soft tissue tumours, thereof 120 sarcomas and 27 aggressive benign lesions were investigated by B-mode and colour Doppler sonography. The echotexture was analysed computer-based using the parameters echogenicity, homogeneity and vascularisation in all lesions.

RESULTS

Different tumour groups showed typical patterns of echotexture, which enabled a classification using 6 categories, distinguishing homogenous hyperechoic, heavily inhomogeneous and homogenous hypoechoic lesions, each group linked to an elevated or low vascularisation. Implementation of the proposed classification revealed a sensitivity in the detection of soft tissue sarcomas and aggressive benign lesions of 94.4 % with a specificity of 79.7 % and an accuracy of 89.7 %.

CONCLUSION

Ultrasonography allows for a determination of the diagnostic and therapeutic procedure in soft tissue tumours. Due to the fact that soft tissue sarcomas present hypervascularised almost exclusively, predominantly homogenous hypoechoic, rarely homogenous hyperechoic, and aggressive benign tumours present homogenous hypoechoic predominantly, such patterns require a biopsy prior to further surgical therapy. However, in homogenous hyperechoic lesions displaying a low blood flow either a primary resection or a conservative treatment with follow-up examinations can be discussed depending on clinical findings and history of the patient. Although the group of heavily inhomogeneous tumours within our collective consisted of benign lesions exclusively, biopsy should be recommended in theses cases in order to exclude a soft tissue sarcoma.

[Classification of soft tissue tumors and current approach to pathologic diagnosis]

Soft tissue sarcomas are rare malignant tumors arising from soft tissues of mesenchymal origin. These tumors can develop from any site in the body, including the extremities, trunk, retroperitoneum, and the head and neck. Factors such as histologic subtype and grade, as well as patient age, tumor size, location and clinical stage, determine the specific approach to management and patient outcome. Early detection and treatment based on accurate diagnosis are the basic principles of the management of soft tissue sarcomas. Although the histological grading of soft tissue sarcomas is based on the French Federation Nationale des Lutte Contre le Cancer (FNCLCC) system, it seems to easy to use the histological grading based on the MIB-1 labeling index. The definitive diagnosis of soft tissue tumors is aided by appropriate immunohistochemical examination and molecular analysis. In particularly, molecular analysis of tumor-specific chromosomal translocations using FISH or RT-PCR methods offers a useful adjunct to the accurate diagnosis of soft tissue tumors. However, many studies have indicated a growing number of fusion gene variations in each tumor type. This article reviews and discusses problems in the diagnostic pathology of soft tissue tumors with newly useful pathological methods.

Analysis of multiple sarcoma expression datasets: implications for classification, oncogenic pathway activation and chemotherapy resistance

Background

Diagnosis of soft tissue sarcomas (STS) is challenging. Many remain unclassified (not-otherwise-specified, NOS) or grouped in controversial categories such as malignant fibrous histiocytoma (MFH), with unclear therapeutic value. We analyzed several independent microarray datasets, to identify a predictor, use it to classify unclassifiable sarcomas, and assess oncogenic pathway activation and chemotherapy response.

Methodology/Principal Findings

We analyzed 5 independent datasets (325 tumor arrays). We developed and validated a predictor, which was used to reclassify MFH and NOS sarcomas. The molecular “match” between MFH and their predicted subtypes was assessed using genome-wide hierarchical clustering and Subclass-Mapping. Findings were validated in 15 paraffin samples profiled on the DASL platform. Bayesian models of oncogenic pathway activation and chemotherapy response were applied to individual STS samples. A 170-gene predictor was developed and independently validated (80-85% accuracy in all datasets). Most MFH and NOS tumors were reclassified as leiomyosarcomas, liposarcomas and fibrosarcomas. “Molecular match” between MFH and their predicted STS subtypes was confirmed both within and across datasets. This classification revealed previously unrecognized tissue differentiation lines (adipocyte, fibroblastic, smooth-muscle) and was reproduced in paraffin specimens. Different sarcoma subtypes demonstrated distinct oncogenic pathway activation patterns, and reclassified MFH tumors shared oncogenic pathway activation patterns with their predicted subtypes. These patterns were associated with predicted resistance to chemotherapeutic agents commonly used in sarcomas.

Conclusions/Significance

STS profiling can aid in diagnosis through a predictor tracking distinct tissue differentiation in unclassified tumors, and in therapeutic management via oncogenic pathway activation and chemotherapy response assessment.

The Rise and Fall of Malignant Fibrous Histiocytoma

The term malignant fibrous histiocytoma was coined by Stout and associates in the 1960s to encompass pleomorphic soft tissue sarcomas presumably derived from histiocytes that are capable of fibroblastic transformation. The concept was reaffirmed in the following 2 decades and malignant fibrous histiocytoma thus was regarded as the most common soft tissue tumor in older adults. However, recent more critical clinicopathologic, ultrastructural, and immunohistochemical studies have shown that malignant fibrous histiocytomas are not derived from histiocytic "facultative fibroblasts" and many neoplasms so diagnosed actually are pleomorphic subtypes of other sarcomas. Meticulous electron microscopic and immunohistochemical investigations also found that the more common storiform-pleomorphic, myxoid, and perhaps the giant cell subtypes are composed of variable mixtures of fibroblasts and phenotypically modulated fibroblastic cells, notably myofibroblasts and histiofibroblasts. On the basis of these findings, we propose a new classification for the above subtypes of so-called malignant fibrous histiocytoma, the majority of which are variants of pleomorphic fibrosarcoma.

[Modern morphological diagnosis and current classification of soft tissue sarcomas]

Malignant soft tissue tumors are somewhat rare, and thus sufficient experience in diagnostics and therapy of these sarcomas is available as a rule only at specialist centers. The gold standard of morphological diagnosis is still represented by evaluation of HE-stained histological sections. However modern methods of examination are also helpful in diagnosis. Because immunohistochemistry is now used routinely, emphasis in this article is laid on molecular methods with special reference to fluorescence in-situ hybridization (FISH) and reverse transcriptase polymerase chain reaction. Principles of the WHO soft tissue tumor classification are explained, and the changed or expanded interpretation of some tumor entities is illustrated using the example of atypical lipomatous tumors, so-called malignant fibrous histiocytomas and hemangiopericytomas, fibrosarcomas, and inflammatory myofibroblastic tumors.

Soft tissue tumors of the prostate: a review

Prostate cancer is a leading cause of cancer-related death in adult men. Some prostates that are suspected to be involved by prostatic adenocarcinoma or nodular prostatic hyperplasia through clinical examination and imaging studies proves on histologic examination to be a soft tissue tumor. This paper outlines the most common soft tissue tumors of the prostate and categorizes them into benign, malignant or miscellaneous. Pathologists must be aware that most, if not all, soft tissue tumors of the body may also be found in the prostate. Diagnostic immunohistochemistry is an important adjunct to histopathology for proper diagnosis and tumor subclassification.

Dendritic cell neoplasms: an overview

Dendritic cell neoplasms are rare tumors that are being recognized with increasing frequency. They were previously classified as lymphomas, sarcomas, or histiocytic neoplasms. The World Health Organization (WHO) classifies dendritic cell neoplasms into five groups: Langerhans' cell histiocytosis, Langerhans' cell sarcoma, Interdigitating dendritic cell sarcoma/tumor, Follicular dendritic cell sarcoma/tumor, and Dendritic cell sarcoma, not specified otherwise (Jaffe, World Health Organization classification of tumors 2001; 273-289). Recently, Pileri et al. provided a comprehensive immunohistochemical classification of histiocytic and dendritic cell tumors (Pileri et al., Histopathology 2002;59:161-167). In this article, a concise overview regarding the pathological, clinical, and therapeutic aspects of follicular dendritic, interdigitating dendritic, and Langerhans' cell tumors is presented.

[Cavernous hemangiomas of the skin of the face and neck and the oral soft tissues]

The structure, clinical manifestations, behavior of cavernous hemangomas of the skin of the face and neck, and the oral soft tissues were studied, by using biopsy specimens from 229 patients. Three types of cavernous hemagiomas of these areas were identified. Their preferred treatments were defined and pathogenetically warranted.

Gene expression profiling of liposarcoma identifies distinct biological types/subtypes and potential therapeutic targets in well-differentiated and dedifferentiated liposarcoma

Classification of liposarcoma into three biological types encompassing five subtypes, (a) well-differentiated/dedifferentiated, (b) myxoid/round cell, and (c) pleomorphic, based on morphologic features and cytogenetic aberrations, is widely accepted. However, diagnostic discordance remains even among expert sarcoma pathologists. We sought to develop a more systematic approach to liposarcoma classification based on gene expression analysis and to identify subtype-specific differentially expressed genes that may be involved in liposarcoma genesis/progression and serve as potential therapeutic targets. A classifier based on gene expression profiling was able to distinguish between liposarcoma subtypes, lipoma, and normal fat samples. A 142-gene predictor of tissue class was derived to automatically determine the class of an independent validation set of lipomatous samples and shows the feasibility of liposarcoma classification based entirely on gene expression monitoring. Differentially expressed genes for each liposarcoma subtype compared with normal fat were used to identify histology-specific candidate genes with an in-depth analysis of signaling pathways important to liposarcoma pathogenesis and progression in the well-differentiated/dedifferentiated subset. The activation of cell cycle and checkpoint pathways in well-differentiated/dedifferentiated liposarcoma provides several possible novel therapeutic strategies with MDM2 serving as a particularly promising target. We show that Nutlin-3a, an antagonist of MDM2, preferentially induces apoptosis and growth arrest in dedifferentiated liposarcoma cells compared with normal adipocytes. These results support the development of a clinical trial with MDM2 antagonists for liposarcoma subtypes which overexpress MDM2 and show the promise of using this expression dataset for new drug discovery in liposarcoma.

Soft tissue sarcoma: An overview

Malignancy of soft tissue, referred to as sarcomas, are some of the rarest tumors in medicine. These tumors account for approximately 1% of all diagnosed malignancies. Diagnosis of soft tissue sarcoma (STS) is a complex process that includes history and physical examination of patient, diagnostic imaging studies, and biopsy when indicated. All clinicians should be able to identify the unique characteristics of malignant soft tissue tumors and assist patients with obtaining care from a specialist in the treatment of STS. Evidence-based medicine has shown that the critical difference in treating STSs is a multidisciplinary approach.

Pathology of Soft Tissue Sarcoma

The evaluation and treatment of soft tissue sarcomas has never been more demanding than it is today. The pathologist plays a central role in this process and is an integral member of the multidisciplinary sarcoma treatment team. This article provides a brief summary of the role of the soft tissue pathologist and includes sections on methods of diagnosis, frozen section, classification of sarcomas, expert consultation, molecular pathology, grading, assessment of treatment response, and tumor banking.

Atypical Lipomatous Tumor, its Variants, and its Combined Forms

Sixty-one cases of neoplasms composed wholly or in part of atypical lipomatous tumor were reviewed. Minimum follow-up was 10 years. The cases were divided into 4 groups based on the findings in the initial excision specimen: conventional atypical lipomatous tumor (n=15), cellular atypical lipomatous tumor (n=21), dedifferentiated liposarcoma (n=24), and atypical lipomatous tumor with a pleomorphic liposarcoma-like component (n=1). The term "cellular atypical lipomatous tumor" was applied to atypical lipomatous tumors having areas of increased cellularity that when non-lipogenic lacked the 5 mitotic figures per 10 high-power fields (maximal rate) required for a dedifferentiated component and when lipogenic fell short of being truly pleomorphic liposarcoma-like. Myxoid regions within this spectrum sometimes had prominent or even plexiform vascularity, creating a resemblance to myxoid liposarcoma especially when interspersed small fat cells were present. The most important prognostic factor was tumor location, as none of the 12 patients with a subcutaneous or intramuscular neoplasm died of tumor. Among the 49 patients with neoplasms of central body sites (mostly retroperitoneum), those with dedifferentiated liposarcoma had significantly shorter survival (median 77 mo) than those with cellular (median 142 mo) or conventional (median 209 mo) atypical lipomatous tumor, whereas there was no statistically significant difference between the latter 2 categories. Patients with atypical lipomatous tumor (either cellular or conventional) in central body sites had significantly shorter survival if the tumor transformed into dedifferentiated liposarcoma in recurrence, and, conversely, those with central body site dedifferentiated liposarcoma had significantly longer survival if it recurred as atypical lipomatous tumor. Metastasis (7 cases) occurred only when the initial specimen or a recurrence demonstrated dedifferentiated liposarcoma.

[Problematic zones in the classification of soft tissue tumors]

The classification of soft tissue tumors is based on the recognition of the resemblance to normal tissue or cells. Nowadays, molecular pathologic findings essentially may contribute to the diagnosis. In daily practice, however, the evaluation of HE sections and immunohistochemical findings are most important because these methods are widely available. Nevertheless, misinterpretations are possible if certain rules and limitations in data utilization for diagnosis are not considered. There are some problematic zones referring to this in which especial attention is mandatory. By means of examples difficulties are explained which may result from overlapping morphological features between soft tissue tumors, between nerve sheath tumors and melanocytic neoplasms, and between soft tissue tumors and sarcomatoid carcinomas. The necessity of a careful interpretation of immunohistochemical findings is underscored with selecting actin positivity as example. Finally, difficulties in determining the dignity of a soft tissue tumor are discussed. Moreover, tumor heterogeneity may under certain conditions render more difficult the classification of a soft tissue tumor.

Proteomic signatures corresponding to histological classification and grading of soft-tissue sarcomas

We performed a global protein expression study on soft-tissue sarcoma in order to develop novel diagnostic biomarkers and allow molecular classification. 2-D difference gel electrophoresis was used to generate the global protein expression profiles of 80 soft-tissue sarcoma samples with seven different histological backgrounds. We found that 67 protein spots distinguished the subtypes of soft-tissue sarcoma. Hierarchical clustering with these 67 protein spots resulted in the grouping of all 80 sarcoma samples corresponding to the histological classification. We found that the expression pattern of tropomyosin isoforms was different in conventional and pleomorphic leiomyosarcomas. We also identified five proteins, including alpha-1-antitrypsin, alpha-actinin 1, HSP27, and elongation factor 2, that could differentiate between malignant fibrous histiocytomas and leiomyosarcomas in grade III into low-risk and high-risk groups, which differed significantly with respect to survival. These results establish proteomics as a powerful tool to develop novel biomarkers for diagnosis and molecular classification of soft-tissue sarcomas. Identification of proteins associated with survival in grade III sarcoma will allow delineation of a high-risk group that may benefit from adjuvant therapy and the exclusion of low-risk patients in whom additional therapies are unlikely to exhibit clinical benefit.

Synovial sarcoma of the extremities: prognostic factors for 20 nonmetastatic cases and a new histologic grading system with prognostic significance

PURPOSE

To evaluate 20 cases of nonmetastatic synovial sarcoma of the extremities regarding prognostic factors, and to propose a histologic grading system with prognostic significance.

METHODS

The cases of 20 patients (14 females and 6 males) with nonmetastatic synovial sarcomas of the extremities treated between 1985 and 1998, were retrospectively evaluated regarding prognostic factors. A histologic grading system with prognostic significance is proposed.

RESULTS

The mean follow-up period was 48.4 months (range, 16-116 months). There was local recurrence in 3 cases (15%), microscopic surgical margin being the only prognostic factor identified. Seven patients (35%) died of the disease in a mean postoperative period of 31.7 months (range, 16-53 months), all with pulmonary or brain metastasis. The survival rate was 65% in 48.4 months of follow-up.

CONCLUSION

The unfavorable prognostic factors identified regarding survival were high histologic grade, tumors proximal to the knee or elbow, and spontaneous tumor necrosis over 25%. Local recurrence did not have influence on survival in this study. The presence of mast cells appears to have a positive influence on survival, although statistical significance was not reached (P = 0.07). The oncologic and functional result was good in 6 cases (30%), regular in 7 (35%), and poor in 7 cases (35%).

[Cutaneous hemangioma: clinical aspects]

Infantile cutaneous hemangioma is a benign vascular tumour present at 10% of the infants. It forms part of the group of the vascular tumours in the classification of International Society for Vascular Anomalies (ISSVA). Clinical diagnosis is easy in its triphasic typical form with a phase of sometimes brutal postnatal growth, a phase of stabilization and a phase of slow secondary regression. Classically, it is presented in the form of a mass or stains cutaneous red, of a subcutaneous mass or, generally, of a mixed form associating the two aspects.

Tumoral, quasitumoral and pseudotumoral lesions of the superficial and somatic soft tissue: new entities and new variants of old entities recorded during the last 25 years. Part XII: appendix

In an eleven part series published in Pathologica, we have presented various tumoral, quasitumoral and pseudotumoral lesions of the superficial and somatic soft tissue (ST), which emerged as new entities or as variants of established entities during the last quarter of a century. Detailed clinicomorphological and differential diagnostic features of approximately sixty entities were chosen on the basis of their clinical significance and morphologic distinctiveness. The series included fibrous and myofibroblastic tumors (e.g. solitary fibrous tumor, high grade classic and pigmented dermatofibrosarcoma protuberans, inflammatory myofibroblastic tumor and myofibrosarcomas), fibromyxoid and fibrohistiocytic neoplasms (e.g., Evans' tumor, phosphaturic mesenchymal tumor, inflammatory myxohyaline tumor), special adipocytic/vascular/and smooth muscle lesions (e.g., chondroid lipoma, Dabska's tumor, ST hemangioblastoma, lipoleiomyosarcoma), epithelioid mesenchymal malignancies of diverse lineages (e.g., epithelioid liposarcoma, proximal-type epithelioid sarcoma, neuroendocrine extraskeletal chondromyxoid sarcoma), ST Ewing's tumor and peripheral nerve sheath tumors (perineuriomas and pigmented and rosetting tumors of the schwannoma/neurofibroma group), extranodal dendritic or histiocytic proliferative processes (follicular dendritic cell sarcoma, Rosai-Dorfman disease, Castleman's disease, and plexiform xanthomatous tumor), and tumors with myoepithelial differentiation. The section devoted to selected pseudotumoral entities considered representatives of the hamartoma group (neural fibrolipomatous hamartoma, ectopic hamartomatous thymoma, rudimentary meningocele), metabolic diseases (amyloid tumor, nephrogenic fibrosing dermopathy, tophaceous pseudogout, pseudoinfiltrative parathyromatosis), stromal tissue reactions to trauma (fibroosseous pseudotumors of digits) and infections (bacillary angiomatosis), and normal organs (glomus coccygeum). To conclude the descriptive phase, supplementary material has now been collected and appended in an attempt to provide a quick digest of essential knowledge both for comparison and differential diagnosis. The data have been tailored to synthesize diverse sources, integrating clinical elements and references to articles that previously appeared in Part I ("Introduction"), Part II ("The List and Review of New Entities") and Parts III to XI ("Excerpta"). At the very least we hope this final part ("Appendix") will provide the reader with a useful tabular organization of ST lesions and a reference resource.

Immunohistochemical Detection of hTERT Protein in Soft Tissue Sarcomas

Human telomerase reverse transcriptase (hTERT) is a telomerase catalytic subunit that regulates telomerase activity. Telomerase is expressed in many human cancers and cell lines and is thought to contribute to their immortality. Little is known about the expression of telomerase in non-epithelial tumors. The objective of this study was to evaluate hTERT expression in a wide range of soft tissue sarcomas. A total of 154 cases of different types of soft tissue sarcoma (54 low-grade, 40 intermediate-grade, and 60 high-grade cases) were evaluated for hTERT expression using immunohistochemistry on tissue microarrays. hTERT immunoexpression was detected in 59% of cases; it was observed in 46%, 58%, and 72% of low-grade, intermediate-grade, and high-grade sarcoma cases, respectively. The intensity of staining positively correlated with the grade of the sarcomas: diffuse strong positive nuclear staining was identified in 6, 8, and 30 cases of low-grade, intermediate-grade, and high-grade sarcomas, respectively. These results suggest that telomerase expression is more often detected in highly malignant tumors than in low-grade sarcomas and thus may be a critical mechanism in tumor progression.

The usefulness of cytogenetic analysis in fine needle aspirates for the histologic subtyping of sarcomas

Conventional cytogenetic analysis performed from open biopsy tissue samples may be a useful adjunct for the histologic subtyping of bone and soft tissue sarcomas. However, its diagnostic utility in fine needle aspiration biopsy (FNAB) specimens is unclear. We retrospectively reviewed 24 consecutive FNAB bone and soft tissue sarcoma specimens, procured from 1995 to 2003, in which aspirated material was obtained for cytogenetic analysis. The study sample included eight Ewing sarcomas, six synovial sarcomas, five rhabdomyosarcomas, two myxoid liposarcomas, and one each of myxoid chondrosarcoma, osteosarcoma, and atypical lipoma. Cytogenetic analysis confirmed the t(X;18) in all six synovial sarcomas and the t(11;22) in three Ewing sarcomas. The t(2;13) was strongly suggested in one alveolar rhabdomyosarcoma. For two of these cases (both of which were synovial sarcomas), cytogenetic analysis was necessary for definitive diagnosis. While the positive cytogenetic results were supportive in the remainder, all were initially and accurately subtyped based on cytomorphology and/or immunohistochemistry. Cytogenetic analysis was noncontributory (eg no growth) in 14 sarcoma cases, but excluding the case of atypical lipoma, this did not preclude the rendering of an accurate diagnosis. Cytogenetic analysis can be performed on FNAB specimens from bone and soft tissue sarcomas and may be a useful diagnostic aid in difficult cases. However, when cell block material is available for immunohistochemistry, the majority of such cases are successfully subtyped.