Histological features and genomic alterations

A retrospective review of six patients with malignant ectomesenchymoma from a single institution identified rhabdomyosarcoma as the mesenchymal element in five of six tumors.[2] Tumors with an alveolar rhabdomyosarcoma morphology exhibited the characteristic translocations, including translocation of the FOXO1 gene fusing with the PAX3 or PAX7 gene. No unifying molecular aberrations were identified.

A single-institution retrospective review identified seven cases of malignant ectomesenchymoma.[1] Most patients showed elements of embryonal rhabdomyosarcoma. The mixed neuroectodermal elements were scattered ganglion cells, ganglioneuroma, or ganglioneuroblastoma. Six of seven cases had HRAS variants. The trimethylation at lysine 27 of histone H3 (H3K27me3), typically lost in malignant peripheral nerve sheath tumor, was retained in all cases.