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Simple Summary: The myogenic differentiation 1 gene (MYOD1) p.L122R mutation was first discovered in a subset of clinically aggressive rhabdomyosarcomas in both adults and children. It occurs most frequently in spindle cell (Sp) or sclerosing (Sc) RMS, but also occasionally in ERMS, including 3% of all PAX fusion-negative RMS. The presence of the MYOD1L122R mutation seems to be associated with a very poor prognosis, especially when it occurs concomitantly with other mutations such as PIK3CA. In this review, we consider the known biological effects of MYOD1 mutations and present a review of published cases of RMS with MYOD1 mutations. Together, the reviewed biological characteristics and the clinical features focus attention on this specific subgroup of patients with poor outcome and highlight the need to identify an optimal therapeutic strategy. Major progress in recent decades has furthered our clinical and biological understanding of rhabdomyosarcoma (RMS) with improved stratification for treatment based on risk factors. Clinical risk factors alone were used to stratify patients for treatment in the European Pediatric Soft Tissue Sarcoma Study Group (EpSSG) RMS 2005 protocol. The current EpSSG overarching study for children and adults with frontline and relapsed rhabdomyosarcoma (FaR-RMS NCT04625907) includes FOXO1 fusion gene status in place of histology as a risk factor. Additional molecular features of significance have recently been recognized, including the MYOD1L122R gene mutation. Here, we review biological information showing that MYOD1L122R blocks cell differentiation and has a MYC-like activity that enhances tumorigenesis and is linked to an aggressive cellular phenotype. MYOD1L122R mutations can be found together with mutations in other genes, such as PIK3CA, as potentially cooperating events. Using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, ten publications in the clinical literature involving 72 cases were reviewed. MYOD1L122R mutation in RMS can occur in both adults and children and is frequent in sclerosing/spindle cell histology, although it is also significantly reported in a subset of embryonal RMS. MYOD1L122R mutated tumors most frequently arise in the head and neck and extremities and are associated with poor outcome, raising the issue of how to use MYOD1L122R in risk stratification and how to treat these patients most effectively. [ABSTRACT FROM AUTHOR]

Intracranial Ewing sarcoma (EwS) is rare and publications on primary or metastatic intracranial EwS are minimal. The aim of this study was to describe incidence, clinical behavior, treatment, and factors associated with outcome in patients with primary intracranial EwS or patients with a primary extracranial EwS and cerebral metastases at diagnosis. We reviewed all patients with primary or with metastatic intracranial EwS at diagnosis registered in the International Clinical Trial Euro-E.W.I.N.G.99 (EE99). In total, 17 of 1435 patients (1.2%) presented with primary intracranial EwS; 3 of them had metastatic disease. Four patients (0.3%) with primary extracranial EwS presented with intracranial metastatic lesions. The 3-year event-free survival (EFS) was 64% and overall survival (OS) was 70% in patients with a primary intracranial EwS. Local control in patients with primary intracranial EwS consisted of surgery (6%), radiotherapy (RT) (18%), or both modalities (76%). Univariate analysis showed that patients < 15 years of age had significantly better outcome (EFS: 72%; OS: 76%) compared to those aged above 15 years (EFS: 13%; OS: 25%). In conclusion, primary intracranial EwS and extracranial EwS with cerebral metastases at diagnosis is rare, yet survival is comparable with local and metastatic EwS elsewhere in the body. Age and stage of disease are important prognostic factors. Besides chemotherapeutic treatment, local control with surgical resection combined with RT is recommended whenever feasible.