Clinico-genetic aspects of a pediatric non-neurofibromatosis type 1 malignant triton tumor with loss of chromosome X

NF1-Driven Rhabdomyosarcoma Phenotypes: A Comparative Clinical and Molecular Study of NF1-Mutant Rhabdomyosarcoma and NF1-Associated Malignant Triton Tumor

PURPOSE

Alterations of the NF1 tumor suppressor gene is the second most frequent genetic event in embryonal rhabdomyosarcoma (ERMS), but its associations with clinicopathologic features, outcome, or coexisting molecular events are not well defined. Additionally, NF1 alterations, mostly in the setting of neurofibromatosis type I (NF1), drive the pathogenesis of most malignant peripheral nerve sheath tumor with divergent RMS differentiation (also known as malignant triton tumor [MTT]). Distinguishing between these entities can be challenging because of their pathologic overlap. This study aims to comprehensively analyze the clinicopathologic and molecular spectrum of NF1-mutant RMS compared with NF1-associated MTT for a better understanding of their pathogenesis.

METHODS

We investigated the clinicopathologic and molecular landscape of a cohort of 22 NF1-mutant RMS and a control group of 13 NF1-associated MTT. Cases were tested on a matched tumor-normal hybridization capture-based targeted DNA next-generation sequencing.

RESULTS

Among the RMS group, all except one were ERMS, with a median age of 17 years while for MTT the mean age was 39 years. Three MTTs were misdiagnosed as ERMS, having clinical impact in one. The most frequent coexisting alteration in ERMS was TP53 abnormality (36%), being mutually exclusive from NRAS mutations (14%). MTT showed coexisting CDKN2A/B and PRC2 complex alterations in 38% cases and loss of H3K27me3 expression. Patients with NF1-mutant RMS exhibited a 70% 5-year survival rate, in contrast to MTT with a 33% 5-year survival. All metastatic NF1-mutant ERMS were associated with TP53 alterations.

CONCLUSION

Patients with NF1-mutant ERMS lacking TP53 alterations may benefit from dose-reduction chemotherapy. On the basis of the diagnostic challenges and significant treatment and prognostic differences, molecular profiling of challenging tumors with rhabdomyoblastic differentiation is recommended.

Malignant triton tumor of the kidney in a child: A case report

Introduction

Malignant triton tumor (MTT) is an extremely rare variant of the malignant peripheral nerve sheath tumors (MPNSTs) with rhabdomyosarcomatous differentiation, which was first described in 1932 by Mason. MTT affects, in most cases, patients under 35 years of age, and it is usually manifested as a mass that may or not be painful. However, the incidence in pediatric patients is atypical. This tumor presents an aggressive course and limited survival rate, and the prognosis is different between individuals with or without a concomitant diagnosis of neurofibromatosis type 1 (NF1). Currently, the recommended treatment is surgical resection, and adjuvant chemotherapy and radiotherapy, but its efficacy is not yet clear.

Presentation of the case

A 13-year-old female patient was referred to the pediatric oncology service due to the presence of an abdominal mass and weight loss, initially diagnosed with Wilms' tumor. After extensive investigation, surgical resection, and immunohistopathological evaluation, the diagnosis of malignant triton tumor was confirmed. The patient also underwent cycles of chemotherapy after resection, and is currently awaiting immunotherapy.

Discussion and conclusion

Malignant triton tumor is extremely rare and difficult to diagnose, especially in children or young people, age groups in which the incidence of the disease is even lower. This may be the reason it is rarely suspected, and it was a great challenge for the clinical care team. It is essential to consider and investigate this possibility of differential diagnosis, as patients diagnosed with this malignant tumor have a low survival rate and poor prognosis.

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Malignant triton tumor (MTT) is an extremely rare histological subtype of MPNSTs.

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MTT is an MPNST with rhabdomyosarcomatous differentiation.

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MTT is an extremely rare type of neoplasia, especially in pediatric patients.

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The kidney is an uncommon growth site of MTT.

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MTT presents a complex anatomopathological and immunohistochemical diagnosis.