A landscape of possibilities to improve the outcome of children affected by Rhabdomyosarcoma

Over the past few decades, many efforts have been made to identify patients with a diagnosis of rhabdomyosarcoma (RMS) and a worse prognosis, in need for more intensive therapy and/or novel treatments. The aim of this work is to focus on this group of patients to build up different strategies from a clinical and a preclinical point of view to help improve their outcome. Accurately categorizing patients into risk groups is crucial for determining the appropriate treatment approach. However, a challenge arises in patients with orbital RMS, where the tumor may erode the bone and extend into the brain, leading to orbital parameningeal (PM) RMS requiring more intense therapy. Existing protocols lack clear guidance on considering varying degrees of bone erosion (BE). Analyzing 199 patients from the RMS2005 trial, we classified BE using an established grade system, revealing a correlation between extensive BE and poorer overall survival. In parallel to patients’ stratification refinements, treatment has progressively improved. The EpSSG RMS2005 trial, showcases the enhanced survival of high-risk patients through the incorporation of maintenance chemotherapy (MC). An extensive literature review and real-world data analysis revealed MC's feasibility and safety. Moreover, we found that MC was customized based on myelotoxicity, but such adjustments did not impact on survival outcomes. With a view to further refine the treatment of patients, for those with a very poor outcome due to a relapsed/refractory RMS, while waiting for new promising compounds, we think there is still the potential to optimize the therapeutic strategy with existing drugs. Consistent with this, we propose a useful chemotherapy strategy for anthracycline naïve patients. Beyond clinical factors and PAX-FOXO fusion status, also other biological characteristics could help in better categorizing patients. Our comprehensive review, encompassing published data and a collaborative study, emphasizes categorizing MYOD1 mutation as a significant risk factor for poorer prognosis, suggesting the need for more intensive treatment—a valuable insight poised for integration into the European treatment protocol. With the aim of deepening our understanding of biological features, this work also focuses on results from Mappyacts program (NCT02613962). Our analysis of 70 patients with relapsed/refractory RMS, showed that 88% had a successful sequencing and 82% of them had at least one potentially targetable alteration. All alterations were "investigational" or "hypothetical," with limited evidence supporting targeted treatment. One hypothesis to explain this low rate of effective treatment suggests that somatic mutations in the Mappyacts cohort are likely, in most cases, passenger events. In line with that, alveolar RMS, PAX-FOXO fusion driven, was taken into account. After a literature search, we identified and tested on preclinical models a compound (CCS1477) potentially hitting the fusion. We showed preliminary activity of CCS1477 as a single agent starting from 1 μM concentration, and a similar perturbation of RMS cell metabolism of IVADo. As a further step beyond genome profiling, a drug screening platform based on five multi-compound plates, prioritized in five tiers, has been built as the final step of this work, where we detail the methodology employed in our laboratory to establish the primary culture system and the list of compounds that we test. In summary, this study provides a comprehensive overview of diverse avenues and potential strategies that can be concurrently pursued to enhance the prognosis of children affected by rhabdomyosarcoma (RMS), especially those confronting high-risk, relapsed, or refractory disease.