Rhabdomyosarcoma in children - current pathologic and molecular classification.

The last 25 years have brought significant progress in the treatment of sarcomas in children, especially rhabdomyosarcoma (RMS). Nevertheless, treatment failure in some patients results from considerable biological heterogeneity noted in these tumours. RMS, the most common malignant soft tissue neoplasm in children, includes two main subtypes: embryonal (ERMS) and alveolar (ARMS). Due to greater aggressiveness and worse prognosis of ARMS in comparison to ERMS, discrimination between different rhabdomyosarcoma subtypes is of crucial clinical importance. This paper presents the current histological classification of RMS, up-to-date immunohistochemical and biological research regarding RMS, and its associated clinical and prognostic significance.

Childhood rhabdomyosarcoma. / Rabdomiosarcoma infantil.

Rhabdomyosarcoma is the most common soft-tissue sarcoma in children; it can appear in any part of the body. Its biological behavior varies widely, and despite the absence of specific clinical or radiological characteristics, rhabdomyosarcoma should be taken into account in the differential diagnosis of solid tumors in children. This review focuses primarily on the imaging findings and anatomical distribution of the histological subtypes of childhood rhabdomyosarcoma and secondarily on the differential findings in histological studies.

Histology, Fusion Status, and Outcome in Alveolar Rhabdomyosarcoma With Low-Risk Clinical Features: A Report From the Children's Oncology Group.

BACKGROUND: Distinguishing alveolar rhabdomyosarcoma (ARMS) from embryonal rhabdomyosarcoma (ERMS) is of prognostic and therapeutic importance. Criteria for classifying these entities evolved significantly from 1995 to 2013. ARMS is associated with inferior outcome; therefore, patients with alveolar histology have generally been excluded from low-risk therapy. However, patients with ARMS and low-risk stage and group (Stage 1, Group I/II/orbit III; or Stage 2/3, Group I/II) were eligible for the Children's Oncology Group (COG) low-risk rhabdomyosarcoma (RMS) study D9602 from 1997 to 1999. The characteristics and outcomes of these patients have not been previously reported, and the histology of these cases has not been reviewed using current criteria. PROCEDURE: We re-reviewed cases that were classified as ARMS on D9602 using current histologic criteria, determined PAX3/PAX7-FOXO1 fusion status, and compared these data with outcome for this unique group of patients. RESULTS: Thirty-eight patients with ARMS were enrolled onto D9602. Only one-third of cases with slides available for re-review (11/33) remained classified as ARMS by current histologic criteria. Most cases were reclassified as ERMS (17/33, 51.5%). Cases that remained classified as ARMS were typically fusion-positive (8/11, 73%), therefore current classification results in a similar rate of fusion-positive ARMS for all clinical risk groups. In conjunction with data from COG intermediate-risk treatment protocol D9803, our data demonstrate excellent outcomes for fusion-negative ARMS with otherwise low-risk clinical features. CONCLUSIONS: Patients with fusion-positive RMS with low-risk clinical features should be classified and treated as intermediate risk, while patients with fusion-negative ARMS could be appropriately treated with reduced intensity therapy.

Integrated genetic and epigenetic analysis defines novel molecular subgroups in rhabdomyosarcoma.

Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma in childhood. Here we studied 60 RMSs using whole-exome/-transcriptome sequencing, copy number (CN) and DNA methylome analyses to unravel the genetic/epigenetic basis of RMS. On the basis of methylation patterns, RMS is clustered into four distinct subtypes, which exhibits remarkable correlation with mutation/CN profiles, histological phenotypes and clinical behaviours. A1 and A2 subtypes, especially A1, largely correspond to alveolar histology with frequent PAX3/7 fusions and alterations in cell cycle regulators. In contrast, mostly showing embryonal histology, both E1 and E2 subtypes are characterized by high frequency of CN alterations and/or allelic imbalances, FGFR4/RAS/AKT pathway mutations and PTEN mutations/methylation and in E2, also by p53 inactivation. Despite the better prognosis of embryonal RMS, patients in the E2 are likely to have a poor prognosis. Our results highlight the close relationships of the methylation status and gene mutations with the biological behaviour in RMS.

Classification of rhabdomyosarcoma and its molecular basis.

Rhabdomyosarcoma (RMS), the most common soft tissue sarcoma in children, has traditionally been classified into embryonal rhabdomyosarcoma (ERMS) and alveolar rhabdomyosarcoma (ARMS) for pediatric oncology practice. This review outlines the historical development of classification of childhood RMS and the challenges that have been associated with it, particularly problems with the diagnosis of "solid variant" ARMS and its distinction from ERMS. In addition to differences in clinical presentation and outcome, a number of genetic features underpin separation of ERMS from ARMS. Genetic differences associated with RMS subclassification include the presence of reciprocal translocations and their associated fusions in ARMS, amplification of genes in ARMS and its fusion subsets, chromosomal losses and gains that mostly occur in ERMS, and allelic losses and mutations usually associated with ERMS. Chimeric proteins encoded in most ARMS from the fusion of PAX3 or PAX7 with FOXO1 are expressed, result in a distinct pattern of downstream protein expression, and appear to be the proximate cause of the bad outcome associated with this subtype. A sizeable minority of ARMS lacks these fusions and shares the clinical and biological features of ERMS. A battery of immunohistochemical tests may prove useful in separating ERMS from ARMS and fusion-positive ARMS from fusion-negative ARMS. Because of limitation of predicting outcome solely based on histologic classification, treatment protocols will begin to utilize fusion testing for stratification of affected patients into low-risk, intermediate-risk, and high-risk groups.

Dense pattern of embryonal rhabdomyosarcoma, a lesion easily confused with alveolar rhabdomyosarcoma: a report from the Soft Tissue Sarcoma Committee of the Children's Oncology Group.

OBJECTIVES: To examine whether the frequency of fusion-negative alveolar rhabdomyosarcoma (ARMSn) increased coincident with changes in the definition of alveolar histology. METHODS: We re-reviewed alveolar rhabdomyosarcoma (ARMS) in the Children's Oncology Group study D9803, comparing histopathology with fusion status. RESULTS: Our review of 255 original ARMS cases (compared with a control group of 38 embryonal rhabdomyosarcomas [ERMS] cases) revealed that many had an ARMS-like densely cellular pattern with cytologic features and myogenin expression more typical of ERMS. Following re-review, 84 (33%) cases of original ARMS were rediagnosed as ERMS. All reclassified ERMS, including dense ERMS, were fusion negative, whereas 82% of confirmed ARMS cases were fusion positive. Total ARMS diagnoses returned to historic rates of 25% to 30% of all rhabdomyosarcomas, and ARMSn decreased from 37% to 18% of ARMS cases. The outcome of reclassified ERMS was similar to confirmed ERMS. CONCLUSIONS: To address the role of fusion status in risk stratification, pathologists should include both a histologic diagnosis and an evaluation of fusion status for all new ARMS diagnoses.

Rhabdomyosarcoma subtyping by immunohistochemical assessment of myogenin: tissue array study and review of the literature.

Myogenin immunostaining has been described as a useful marker of the alveolar subtype of rhabdomyosarcoma and as a tool for distinguishing it from the more common embryonal subtype. To add to the growing body of literature describing this phenomenon we analysed myogenin immunohistochemical staining in 152 tumors using a rhabdomyosarcoma tissue array. Results were analysed blinded to histological type by two independent investigators. Samples were excluded if any samples failed to stain with desmin and/or myogenin. Mean percentage of myogenin positive cells was significantly greater for ARMS (n = 31; mean percentage positivity 59% (95% confidence intervals +/- 7%) than ERMS (n = 41, mean percentage positivity 16%, 95% confidence intervals +/- 4; P < 0.0001). This data is consistent with previously published studies identifying strong nuclear myogenin staining in a high proportion of cells as a marker of alveolar histology.

Different expression profiles of Y-box-binding protein-1 and multidrug resistance-associated proteins between alveolar and embryonal rhabdomyosarcoma.

Nuclear expression of the Y-box-binding protein-1 (YB-1) has been reported to regulate the expression of both P-glycoprotein (P-gp) and major vault protein (MVP), and to regulate proliferative activities in human malignancies. Based on morphology and molecular biology, rhabdomyosarcoma (RMS) can be divided into two major types: embryonal type and the more aggressive alveolar type. Thirty-five cases of embryonal RMS (ERMS) and 28 cases of alveolar RMS (ARMS) were examined immunohistochemically for the nuclear expression of YB-1 and the intrinsic expression of P-gp, multidrug resistance (MDR)-associated protein (MRP) 1, 2, and 3, breast-cancer resistant protein (BCRP) and MVP, and the findings were compared with proliferative activities as evaluated by the MIB-1-labeling index (LI). Moreover, mRNA levels of these MDR-related molecules were assessed using a quantitative reverse transcriptase-PCR method in 18 concordant frozen materials. P-gp expression was more frequently observed ARMS, compared with ERMS (P = 0.0332), whereas immunoreactivity for BCRP was more frequently recognized in ERMS (P = 0.0184). Nuclear expression of YB-1 protein was correlated with P-gp (P = 0.0359) and MVP (P = 0.0044) expression, and a higher MIB-1-labeling index (P = 0.0244) in ERMS, however, in ARMS no such relationships were observed. These immunohistochemical results indicate that different expression profiles of MDR-related molecules and their correlation with YB-1 nuclear expression support the concept that ERMS and ARMS are molecular biologically distinct neoplasms. Apart from ERMS, frequent P-gp expression in ARMS may be independent from YB-1 regulation. However, YB-1 may be a candidate for a molecular target in rhabdomyosarcoma therapy, especially in ERMS.

[Sclerosing rhabdomyosarcoma: a clinicopathologic study of four cases with review of literature].

OBJECTIVE: To study the clinicopathologic characteristics of sclerosing rhabdomyosarcoma (SRMS) and its distinction from embryonal rhabdomyosarcoma (ERMS) and alveolar rhabdomyosarcoma (ARMS). METHODS: The clinical, histologic and immunohistochemical features of 4 cases of SRMS were studied. The literature was reviewed. RESULTS: All the 4 cases occurred in adults. The age of patients ranged from 20 to 54 years (mean = 41.5 years). The male-to-female ratio was 1:1. The tumor was located in the left wrist, right thigh, right face and right cheek respectively and the tumor size varied from 2.5 cm to 10 cm in dimension (mean = 5.7 cm). Histologically, SRMS was characterized by the presence of large amounts of heavily hyalinized matrix, mimicking osteoid or chondroid tissue. The tumor cells were composed predominantly of primitive small round cells which were arranged in diverse growth patterns, including fascicular, cord-like, single-file, trabecular, microalveolar and pseudovascular structures. A few rhabdomyoblasts were identified in 1 case. A second spindle cell component was focally found in 2 cases, resembling spindle cell rhabdomyosarcoma or peripheral nerve sheath tumor. Immunohistochemically, all cases showed diffuse staining for Myo D1 and focal staining for desmin. The staining for myogenin was often negative. Three of the cases also expressed muscle-specific actin and 2 cases were positive for alpha-smooth muscle actin. They were all negative for h-caldesmon, S-100 protein, CD31, CD34, AE1/AE3 and anaplastic lymphoma kinase protein. CONCLUSIONS: SRMS differs from ERMS and ARMS morphologically. Recent cytogenetic studies however suggest a histogenetic relationship with ERMS. Familiarity with its morphologic features and immunophenotype may help to distinguish this peculiar variant of rhabdomyosarcoma from a variety of lesions with abundant sclerosing matrix.

Actin isoform pattern expression: a tool for the diagnosis and biological characterization of human rhabdomyosarcoma.

The diagnosis and characterization of rhabdomyosarcoma requires the use of combined histological and immunohistochemical criteria due to the variety of its histological patterns. The identification of actin isoform expression is accepted as a useful adjunct to the diagnosis and classification of soft tissue tumors. Using a new antibody specific for alpha-cardiac actin, obtained according to a recently described strategy for the production of polyclonal antibodies against actin isoforms [9], we have analyzed a series of 17 rhabdomyosarcomas, including all histological subtypes. In addition, we have evaluated the presence in these tumors of alpha-skeletal and alpha-smooth muscle actins. All specimens examined revealed a positive immunostaining for alpha-cardiac actin. Tumoral cells of eight cases also expressed alpha-smooth muscle actin and only three cases (all embryonal subtypes) were positive for alpha-skeletal actin. Our results indicate that immunohistochemical screening for alpha-cardiac actin expression is a useful tool for the diagnosis of rhabdomyosarcoma. They also suggest that the expression of alpha-skeletal actin is valuable in determining the subtype and possibly the state of differentiation of these tumors.

Value of image cytometry in the subclassification of rhabdomyosarcoma.

OBJECTIVE: To test the discriminatory capability of nuclear features in the subclassification of rhabdomyosarcoma (RMS) and especially to differentiate embryonal from alveolar RMS. STUDY DESIGN: The study included 42 patients with RMS. We performed the analysis on Feulgen-stained filtrates of cell suspensions prepared from deparaffinized tissue sections. Image analysis was performed by an automated, high-resolution image cytometer on at least 200 nuclear images. Photometric, morphometric and nuclear texture features were analyzed. Probability density distributions were calculated for each nuclear feature of individual RMS subgroups and compared in order to detect possible differences. RESULTS: There were significant differences between embryonal and alveolar RMS in five nuclear features: DNA index, sphericity, elongation, low_DNA_area and fractall_area. We were able to differentiate between the two main RMS subgroups in 82% of cases on the basis of either sphericity or elongation alone, while the power of differentiation for texture features was 72-79%. CONCLUSION: Differentiation between embryonal and alveolar RMS using one nuclear feature is not an important adjunct to light microscopy. However, the possibility of using a combination of nuclear features would probably increase the discriminatory ability.

Rabdomiosarcoma embrionario nasal: actualización / Nasal embryonal rhabdomyosarcoma: update

El rabdomiosarcoma no es sólo el sarcoma de tejidos blandos más común en los niños menores de 15 años, sino también en adolescentes y adultos jóvenes. Presentamos el caso de un paciente de sexo masculino de 12 años de edad, quien desarrolló un tumor polipoideo que protruía en la fosa nasal derecha, diagnosticándose rabdomiosarcoma embrionario. Se realiza tratamiento quirúrgico y quimioterápico con muy buen resultado. El paciente después de dos años de su diagnóstico se encuentra libre de enfermedad. Realizamos una revisión de esta variante histopatológica de rabdomiosarcoma, su pronóstico y tratamiento

Rabdomiosarcoma embrionario nasal: actualización / Nasal embryonal rhabdomyosarcoma: update

El rabdomiosarcoma no es sólo el sarcoma de tejidos blandos más común en los niños menores de 15 años, sino también en adolescentes y adultos jóvenes. Presentamos el caso de un paciente de sexo masculino de 12 años de edad, quien desarrolló un tumor polipoideo que protruía en la fosa nasal derecha, diagnosticándose rabdomiosarcoma embrionario. Se realiza tratamiento quirúrgico y quimioterápico con muy buen resultado. El paciente después de dos años de su diagnóstico se encuentra libre de enfermedad. Realizamos una revisión de esta variante histopatológica de rabdomiosarcoma, su pronóstico y tratamiento (AU)

[Bladder embryonal rhabdomyosarcoma in the adult]. / Rabdomiosarcoma embrionario vesical del adulto.

Embryonal rhabdomyosarcoma of the bladder is a tumor thar presents sporadically in the adult patient and its treatment continues to be a controversy. One such case is presented herein. The epidemiological and histopathological features of this tumor type are described and the different therapeutic approaches advocated in the literature are discussed.