An integrative morpho-molecular approach in malignant ectomesenchymoma diagnosis: report of a new paediatric case and a review of the literature.

Introduction: Malignant ectomesenchymoma (MEM) is a soft tissue tumour, consisting of both malignant neuroectodermal elements and one or more mesenchymal elements. Case presentation and review of the literature: Here we describe the case of a 6-months-old male, previously treated in another hospital for abdominal rhabdomyosarcoma (RMS). Histological re-examination demonstrated that the tumour had mesenchymal and neuroectodermal elements components, with a new diagnosis of abdominal-pelvic MEM. A Next-Generation Sequencing (NGS) analysis was performed on a surgical tumour specimen and revealed the presence of a somatic mutation, already reported in MEM cases. We carried out a review of the literature and we found 33 new cases of MEM since the last review. We reported the clinic-pathologic features of new cases of MEM, highlighting the role of molecular studies in supporting the diagnosis of this ambiguous tumours. Conclusion: We promote the importance of a diagnosis based on an integrative morpho-molecular approach, that routinely include molecular analysis and the use of bioinformatic mutation detection tools, to support diagnostic and therapeutical queries and to highlight tumour biology and behaviour.