Undifferentiated rhabdomyosarcoma with lymphoid phenotype expression

Modern Diagnosis of Small Cell Malignancies of Children

Small cell malignancies of children constitute a continuing diagnostic challenge for surgical pathologists, although modern methods of ancillary diagnosis provide powerful tools that resolve most difficult cases. Current techniques range from identification of DNA alternations, including gene fusions, chromosome translocations, and genetic deletions, to recognition of characteristic patterns of protein expression, usually visualized with immunohistochemistry. In spite of these advances, recognition of key cellular and histologic features remains the keystone of diagnosis but requires adequately fixed and carefully stained histologic sections. Cytologic features now suffice for diagnosis if confirmed by appropriate testing. This article outlines key histologic features of pediatric small cell neoplasms and the algorithms that allow diagnostic confirmation and the initiation of appropriate therapy.

Alveolar rhabdomyosarcoma of the head and neck region in older adults: genetic characterization and a review of the literature

Alveolar rhabdomyosarcoma is remarkably rare in adults older than 45 years. Initial immunoprofiling of a small cell neoplasm of the head and neck region in an older adult may not include myogenic markers. A valuable diagnostic aid and important prognostic parameter in alveolar rhabdomyosarcoma is the identification of PAX3-FOXO1 [t(2;13)(q35;q14)] or PAX7-FOXO1 [t(1;13)(p36;q14)] rearrangements. The purpose of this study was to document the clinicopathologic, immunophenotypic, and genetic features of head/neck alveolar rhabdomyosarcoma in older adults. Prior isolated descriptions of 3 patients were included. Five patients were female and 2 male (median age, 61 years). Each neoplasm was composed of undifferentiated, small round cells in a predominantly solid pattern. Initially, ordered immunostains corresponded with early diagnostic impressions of a hematologic malignancy or neuroendocrine carcinoma. CD56 was positive in 5 of 5 tumors and synaptophysin in 1 of 6. Given the virtual absence of other lymphoid or epithelial markers, muscle immunostains were performed and these were positive. Definitive alveolar rhabdomyosarcoma diagnoses were confirmed genetically. This study illustrates the diagnosis of head/neck alveolar rhabdomyosarcoma in older adults is complicated by its rarity, lack of an alveolar pattern, and a potentially misleading immunoprofile (CD56 and synaptophysin immunoreactivity) if myogenic markers are not used. Both PAX3- and PAX7-FOXO1 alveolar rhabdomyosarcomas were identified in these patients. In children, PAX7-FOXO1 alveolar rhabdomyosarcoma is associated with a significantly longer event-free survival. In contrast, adult alveolar rhabdomyosarcoma behaves more aggressively with a worse overall survival than pediatric alveolar rhabdomyosarcoma. Further follow-up and additional cases are required to assess the prognostic relevance of these fusion transcripts in the context of advanced age.

PAX3-FOXO1 fusion gene in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood and adolescence. The predominant histologic variants of this disease are termed embryonal (eRMS) and alveolar (aRMS), based on their appearance under light microscopy. Of the two, aRMS is associated with an more aggressive disease pattern and a higher mortality, mandating a better understanding of this cancer at the molecular level. The PAX3-FOXO1 fusion gene, resulting from the stable reciprocal translocation of chromosomes 2 and 13, is a signature genetic change found only in aRMS, and thought to be responsible at least in part for its malignant phenotype. This review will discuss the clinical significance of the PAX3-FOXO1 fusion gene, the pertinent historical and current models used to study its oncogenic contributions, the transcriptional targets that are thought to mediate these contributions, and the cellular mechanisms impacted by PAX3-FOXO1 that ultimately lead to aRMS.

Rhabdomyosarcomas in adults and children: an update

CONTEXT

Rhabdomyosarcomas comprise a relatively common diagnostic entity among childhood cancers and a relatively rare one among adult tumors. They may possess a variety of histologies that generally differ among age groups. These lesions appear to be separate biologic entities as well as morphologic categories, with embryonal tumors having genetic lesions related to loss of heterozygosity and aberrant parental imprinting, alveolar tumors containing genetic fusions between PAX and forkhead genes, and pleomorphic tumors showing an accumulation of genetic lesions similar to other adult high-grade sarcomas.

OBJECTIVE

To present guidelines for diagnosis of rhabdomyosarcoma and recent finding concerning the biology and classification of these lesions.

DATA SOURCES

Review of recent and older published literature and distillation of the authors' experience.

CONCLUSIONS

Infants and young children tend to have embryonal rhabdomyosarcomas, adolescents and young adults tend to have alveolar rhabdomyosarcomas, and older adults tend to have pleomorphic rhabdomyosarcomas, although there is some overlap. Newer rare entities, including spindle cell rhabdomyosarcoma and sclerosing rhabdomyosarcoma, have been described in children and adults. Fusion-positive tumors have a distinct molecular signature with downstream activation of a number of myogenic and tumorigenic factors. Genetic testing may be successfully used for diagnosis and may guide therapy in future clinical trials. Differential diagnosis has become simpler than in previous years, because of use of myogenic factors in immunohistochemistry, but classification based solely on histologic features remains challenging.

Rhabdomyosarcoma of the head and neck in children

OBJECTIVE

The purpose of this study was to determine the rhabdomyosarcoma types involving the head and neck (H&N) region in children and their immunophenotype.

DESIGN

Anatomic pathology archives at Texas Children's Hospital were searched for all rhabdomyosarcoma cases over a 20-year period. One-hundred and thirty-seven cases were identified, with 50 being H&N cases. The cases were typed according to the Intergroup Rhabdomyosarcoma Study (IRS) criteria. Immunocytochemistry for myogenic and non-myogenic markers was performed on all H&N cases. Electron micrographs from cases (n=32) where ultrastructural examination had been performed at the time of original diagnosis were reviewed.

RESULTS

Children with H&N rhabdomyosarcomas had a mean age of 5.3 years (median 4 years). There was a male predilection (1.7M:1.0F). Primary tumor sites were: face NOS (18%), orbit/periorbital (16%), nasal cavity/nose (14%), lymph nodes (12%), paranasal sinuses (10%), parameningeal (10%), parotid gland (6%), neck (6%), infratemporal fossa/zygoma (2%), buccal mucosa (2%), palate (2%), and larynx (2%). Metastatic disease at diagnosis (33% of all cases) occurred in the bone marrow (11%), cerebrospinal fluid (6%), peritoneal fluid (6%), lung (4%), parietal pleura (2%), pleural fluid (2%) and pericardial fluid (2%). Rhabdomyosarcoma types (IRS criteria) were: embryonal (60%), alveolar (classic and solid subtypes, 28%), botryoid (4%), undifferentiated (4%), spindle cell (2%) and anaplastic (2%). Immunocytochemical findings were: polyclonal desmin (96%); myogenin (96%); muscle-specific actin (74%), smooth muscle actin (12%). Nonmyogenic markers included: vimentin (100%), CD99 (16%), p53 (16%), pancytokeratin (10%), NSE (8%), LCA (6%), CD20 (6%), EMA (2%), and NB-84 (0%, neuroblastoma). Undifferentiated sarcoma expressed only vimentin. By ultrastructural examination, 44% had readily identified z-bands and myofilaments, 37% had infrequent to rare myofilaments and z-bands, and 19% had myotubular intermediate filaments.

CONCLUSIONS

Distribution of H&N rhabdomyosarcoma IRS types is similar to that for all primary sites, with the exception that embryonal types are modestly increased while alveolar type is mildly decreased. There are many non-myogenic immunocytochemical markers that cross-react with rhabdomyosarcoma. Differentiation between favorable and unfavorable rhabdomyosarcoma types is important for appropriate therapy, and predicting prognosis and survival.

Pathologic classification of rhabdomyosarcomas and correlations with molecular studies

Rhabdomyosarcoma, the most common soft-tissue malignancy of childhood and adolescence, comprises a group of differing pathobiologic entities linked by their common propensity for formation of neoplastic skeletal muscle, a feature that results from biological forces related to aberrant transcription signals and the resultant production of myogenic proteins. At a molecular level, however, rhabdomyosarcomas form a heterogeneous group that can be subdivided into distinct clinicopathologic entities based on morphologic appearance and genetic makeup. These differing morphologic features were recognized in the mid-1900s by Horn and Enterline with their division of rhabdomyosarcomas into embryonal, alveolar, botryoid, and pleomorphic subtypes. More recent histologic and biologic studies have resulted in description of additional entities, such as spindle cell and anaplastic rhabdomyosarcoma, and refinements in recognition of the original entities, such as solid-alveolar rhabdomyosarcoma. Familiarity with newer classifications and their relationship to molecular aberrations is key to stratifying patients on current therapeutic protocols and proposed innovative genetic therapies.

Diagnostic gold standard for soft tissue tumours: morphology or molecular genetics?

The recognition of recurrent genetic alterations in specific tumour types has provided the basis for the reclassification of certain soft tissue neoplasms, and molecular analysis of patient material has the potential to provide both diagnostic and prognostic information. In this review, we evaluate the role of molecular genetic testing as the prospective 'gold standard' for sarcoma diagnosis. Molecular genetic testing, as with every new method, promises to improve accuracy and to be more sensitive and less subjective, claims that have been made previously by histochemistry, electron microscopy and immunohistochemistry. Technical limitations in molecular assays, as well as more general specificity issues, decrease the clinical usefulness of molecular pathological testing significantly and suggest that, at present, molecular evaluation is best considered an ancillary technique that neither supersedes other ancillary techniques nor eclipses traditional pathological examination.