Pleomorphic rhabdomyosarcoma in children: four cases in the pediatric age group

Rhabdomyosarcoma: Updates on classification and the necessity of molecular testing beyond immunohistochemistry

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and adolescents under the age of 20. The current World Health Organization (WHO) classification for soft tissue and bone tumors recognizes 4 distinct subtypes of RMS based on clinicopathological and molecular genetic features: embryonal, alveolar, spindle cell/sclerosing and pleomorphic subtypes. However, with the increased use of molecular techniques, the classification of rhabdomyosarcoma has been evolving rapidly. New subtypes such as osseus RMS harboring TFCP2/NCOA2 fusions or RMS arising in inflammatory rhabdomyoblastic tumor have been emerging within the last decade, adding to the complexity of diagnosing skeletal muscle tumors. This review article provides an overview of classically recognized distinctive subtypes as well as new, evolving subtypes and discusses important morphologic, immunophenotypic and molecular genetic features of each subtype including recommendations for a diagnostic approach of malignant skeletal muscle neoplasms.

Genomic profiling of pleomorphic rhabdomyosarcoma reveals a genomic signature distinct from that of embryonal rhabdomyosarcoma

Pleomorphic rhabdomyosarcoma (PRMS) is a rare and highly aggressive sarcoma, occurring mostly in the deep soft tissues of middle-aged adults and showing a variable degree of skeletal muscle differentiation. The diagnosis is challenging as pathologic features overlap with embryonal rhabdomyosarcoma (ERMS), malignant Triton tumor, and other pleomorphic sarcomas. As recurrent genetic alterations underlying PRMS have not been described to date, ancillary molecular diagnostic testing is not useful in subclassification. Herein, we perform genomic profiling of a well-characterized cohort of 14 PRMS, compared to a control group of 23 ERMS and other pleomorphic sarcomas (undifferentiated pleomorphic sarcoma and pleomorphic liposarcoma) using clinically validated DNA-targeted Next generation sequencing (NGS) panels (MSK-IMPACT). The PRMS cohort included eight males and six females, with a median age of 53 years (range 31-76 years). Despite similar tumor mutation burdens, the genomic landscape of PRMS, with a high frequency of TP53 (79%) and RB1 (43%) alterations, stood in stark contrast to ERMS, with 4% and 0%, respectively. CDKN2A deletions were more common in PRMS (43%), compared to ERMS (13%). In contrast, ERMS harbored somatic driver mutations in the RAS pathway and loss of function mutations in BCOR, which were absent in PRMS. Copy number variations in PRMS showed multiple chromosomal arm-level changes, most commonly gains of chr17p and chr22q and loss of chr6q. Notably, gain of chr8, commonly seen in ERMS (61%) was conspicuously absent in PRMS. The genomic profiles of other pleomorphic sarcomas were overall analogous to PRMS, showing shared alterations in TP53, RB1, and CDKN2A. Overall survival and progression-free survival of PRMS were significantly worse (p < 0.0005) than that of ERMS. Our findings revealed that the molecular landscape of PRMS aligns with other adult pleomorphic sarcomas and is distinct from that of ERMS. Thus, NGS assays may be applied in select challenging cases toward a refined classification. Finally, our data corroborate the inclusion of PRMS in the therapeutic bracket of pleomorphic sarcomas, given that their clinical outcomes are comparable.

Pleomorphic Rhabdomyosarcoma: A Systematic Review with Outcome Analysis and Report of a Rare Abdominal Wall Lesion

Introduction. Pleomorphic rhabdomyosarcoma (RMS) is an aggressive and rare malignant neoplasm with a poor prognosis. As its name suggests, this tumor exhibits extensive pleomorphism with features of skeletal muscle differentiation. Due to its rarity, its diagnosis is often a clinical and pathological challenge. Since only small case series and a few scattered case reports exist in the literature, the impact of different demographic features, tumor site, and/or treatment modality on patient outcomes has yet to be extensively studied. Methods. We report a case of a pleomorphic RMS presenting atypically as an abdominal wall mass. We have also analyzed the National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) database to determine the factors affecting the outcome of this neoplasm. Moreover, we present a review and summary of pleomorphic RMS cases arising from the abdominal wall reported in the English language literature. Results. We found two hundred and forty-two cases of pleomorphic RMS in the SEER database. The majority of the patients were diagnosed after the age of 40, with the age of diagnosis showing a unimodal distribution. The majority of the patients were Caucasian (82%) and male (59%). Age of diagnosis, tumor stage, and surgical management significantly affected the patients' outcome, while patients' ethnicity, sex, or tumor site did not affect the outcome. We only found five previously reported cases of pleomorphic RMS arising from the abdominal wall. Conclusions. Pleomorphic RMS arising from the abdominal wall is extremely rare. Our data sheds light on the factors affecting the outcome of pleomorphic RMS. We have also discussed the challenges involving the histopathological diagnosis of this rare neoplasm and how to best approach this task.

Head and Neck Rhabdomyosarcoma: Clinical and Pathologic Characterization of Seven Cases

Head and neck rhabdomyosarcoma occurs frequently in children and adolescents, and has been well studied in that population. In contrast, it is rare in adults and is not as well characterized clinically and pathologically. Seven cases of adult rhabdomyosarcoma occurring in head and neck were retrieved from the archives of Department of Pathology and Division of Oral Pathology at University of Washington. Radiologic findings and clinical history, as well as pathologic findings from hematoxylin and eosin slides and immunohistochemistry for myogenic markers were reviewed. A total of seven cases of rhabdomyosarcoma (two embryonal, three alveolar and two pleomorphic subtype) were reviewed. Patient ages ranged from 18 to 57 years (median 21 years). Classic and unique histologic features for each subtype, including post-treatment morphologic changes, were identified. Clinical follow-up information was available for 4 patients. 3 of 4 patients experienced recurrence, including two with distant metastasis. One patient died of disease progression 41 months after presentation. Head and neck rhabdomyosarcoma in adults can manifest both classic and unique histologic features for each subtype. In addition, recurrence and distant metastasis were observed, suggesting aggressive clinical behavior regardless of subtype.

Epithelioid rhabdomyosarcoma: a clinicopathological study of seven additional cases supporting a distinctive variant with aggressive biological behaviour

We present our experience with seven cases of epithelioid rhabdomyosarcoma (RMS) to further characterise its clinicopathological features. There were five males and two females with ages ranging from 19 to 84 years (mean 56 years). Four tumours occurred in the somatic soft tissue, two in organs and one in the bone. The mean tumour size was 10.7 cm (range 3.5-15 cm). Histologically, six tumours were characterised by sheet-like growth of uniform epithelioid cells with large vesicular nuclei, prominent nucleoli, high mitotic activity and moderate to abundant amphophilic-to-eosinophilic cytoplasm. One tumour was composed of dyscohesive cells with rhabdoid appearance embedded in a myxoid matrix. Features suggestive of rhabdomyoblastic differentiation were absent. However, immunohistochemical study revealed skeletal muscle differentiation in all cases. Of note, focal expression of epithelial markers with co-expression of neuroendocrine markers was noted in five and three cases, respectively. Of six patients with follow-up, one experienced local recurrence and three developed metastases. To date, three patients have died of disease within 14 months. This study further demonstrates that epithelioid RMS represents a distinct variant of RMS with an aggressive behaviour. It may be misdiagnosed as poorly differentiated neuroendocrine carcinoma due to co-expression of epithelial and neuroendocrine markers.

An Increased Risk of Second Malignant Neoplasms After Rhabdomyosarcoma: Population-Based Evidence for a Cancer Predisposition Syndrome?

BACKGROUND

Rhabdomyosarcoma survivors have an increased risk of developing second malignant neoplasms (SMN); this risk is traditionally attributed to the effects of multidisciplinary management required for cure. However, the impact of constitutional predisposition has not been properly analyzed.

METHODS

We analyzed the risk of SMN among 1,151 children diagnosed with rhabdomyosarcoma and reported to the Surveillance, Epidemiology, and End Results registries (SEER-9) from 1973 to 2010. Standardized incidence ratios (SIR) and corresponding 95% confidence intervals (CI) were calculated using SEERStat 8.1.2.

RESULTS

Children with pleomorphic and embryonal rhabdomyosarcoma had an increased risk of developing a SMN (SIR = 15.77, 95%CI 1.91-56.96 and SIR = 5.6, 95%CI 3.32-8.85, respectively). The risk was age-dependent; the highest was among children <2 years (SIR = 13.38, 95%CI 4.34-31.22) and the lowest was in children >10 years (SIR = 3.35, 95%CI 1.53-6.35). The risk for the youngest patients was higher for those with embryonal rhabdomyosarcoma (SIR = 14.72, 95%CI 4.01-37.70) compared to other histiotypes. Additionally, the risk of SMN was independent of the use of radiation to the primary (SIR = 6.50, 95%CI 3.97-10.03 and SIR = 4.57, 95%CI 2.09-8.68, for children receiving and not receiving radiation, respectively). The pattern of SMN observed was consistent with the Li-Fraumeni spectrum.

CONCLUSIONS

Children with rhabdomyosarcoma are at high risk of developing SMN. This risk is higher for a subgroup of young children with pleomorphic and embryonal histologies, and is independent of the use of radiation. This suggests that a subgroup of children with pleomorphic and embryonal rhabdomyosarcoma may have a constitutional cancer predisposition.

Dystrophin and dysferlin double mutant mice: a novel model for rhabdomyosarcoma

Although researchers have yet to establish a link between muscular dystrophy (MD) and sarcomas in human patients, literature suggests that the MD genes dystrophin and dysferlin act as tumor suppressor genes in mouse models of MD. For instance, dystrophin-deficient mdx and dysferlin-deficient A/J mice, models of human Duchenne MD and limb-girdle MD type 2B, respectively, develop mixed sarcomas with variable penetrance and latency. To further establish the correlation between MD and sarcoma development, and to test whether a combined deletion of dystrophin and dysferlin exacerbates MD and augments the incidence of sarcomas, we generated dystrophin and dysferlin double mutant mice (STOCK-Dysf(prmd)Dmd(mdx-5Cv)). Not surprisingly, the double mutant mice develop severe MD symptoms and, moreover, develop rhabdomyosarcoma (RMS) at an average age of 12 months, with an incidence of >90%. Histological and immunohistochemical analyses, using a panel of antibodies against skeletal muscle cell proteins, electron microscopy, cytogenetics, and molecular analysis reveal that the double mutant mice develop RMS. The present finding bolsters the correlation between MD and sarcomas, and provides a model not only to examine the cellular origins but also to identify mechanisms and signal transduction pathways triggering development of RMS.

Soft tissue sarcomas with complex genomic profiles

Soft tissue sarcomas (STS) with complex genomic profiles (50% of all STS) are predominantly composed of spindle cell/pleomorphic sarcomas, including leiomyosarcoma, myxofibrosarcoma, pleomorphic liposarcoma, pleomorphic rhabdomyosarcoma, malignant peripheral nerve sheath tumor, angiosarcoma, extraskeletal osteosarcoma, and spindle cell/pleomorphic unclassified sarcoma (previously called spindle cell/pleomorphic malignant fibrous histiocytoma). These neoplasms show, characteristically, gains and losses of numerous chromosomes or chromosome regions, as well as amplifications. Many of them share recurrent aberrations (e.g., gain of 5p13-p15) that seem to play a significant role in tumor progression and/or metastatic dissemination. In this paper, we review the cytogenetic, molecular genetic, and clinicopathologic characteristics of the most common STS displaying complex genomic profiles. Features of diagnostic or prognostic relevance will be discussed when needed.

Primary osseous rhabdomyosarcoma with focal matrix formation mimicking osteosarcoma

We present an unusual case of primary osseous pleomorphic rhabdomyosarcoma with focal matrix formation mimicking osteosarcoma. The patient was a 21-year-old man who had suffered from pain and slight enlargement of his left calf for 2 months. A plain radiograph demonstrated a large, predominantly osteolytic mass in the region of the proximal fibula with features typical of malignant primary bone tumor. On open surgical biopsy, the tumor consisted of atypical cells, some of them presenting spindle morphology. Between them, there were bands of densely hyalinized matrix with osteoid appearance, but without definite lacunae or calcifications, and an osteosarcoma was diagnosed. Consequently, the tumor was removed. The postoperative tissue presented more pleomorphic cells with some definite rhabdomyoblasts. Desmin, actin, Myf4, and MyoD1 were positive in tumor cells, and a diagnosis of rhabdomyosarcoma was eventually made. Only few cases of primary pure bone rhabdomyosarcoma have been reported. Other bone tumors with rhabdomyosarcomatous differentiation have been described: dedifferentiated chondrosarcoma, fibrosarcoma, and osteosarcoma. Our case does not meet the criteria for sclerosing rhabdomyosarcoma, as matrix formation is focal and cells are spindle-shaped and pleomorphic. However, it is a further example of a diagnostic error in connection with primary osseous tumor.