Embryonal rhabdomyosarcoma


Embryonal rhabdomyosarcoma is a rare histological form of cancer of connective tissue wherein the mesenchymally-derived malignant cells resemble the primitive developing skeletal muscle of the embryo. It is the most common soft tissue sarcoma occurring in children. ERMS is also known as Fusion-Negative rhabdomyosarcoma, as tumors of this subtype are unified by their lack of a PAX3-FOXO1 fusion oncogene.

Classification

ERMS is the more common of two major sub-types of rhabdomyosarcoma, the other being alveolar rhabdomyosarcoma also known as Fusion Positive RMS. Commonly, FN-RMS is driven by a mutation in the RAS family of proto-oncogenes, creating a powerful signal which is now known to promoter tumor growth by preventing muscle lineage progression by blocking expression of the transcription factor MYOG. Inhibition of this signaling pathway with trametinib has been recently shown to overcome this differentiation block and reduce tumor progression in animal models of FN-RMS.
FN-RMS has been informally classified as a "small round blue cell tumor" because of the characteristic microscopic appearance of its cells after histological staining with hematoxylin and eosin.

Prognosis

The prognosis for rhabdomyosarcoma has improved greatly in recent decades, with over 70% of patients surviving for five years after diagnosis. Nevertheless, some FN-RMS patients with a rare Leu122Arg mutation in MYOD1 gene have very poor outcome.