SOLID ALVEOLAR RHABDOMYOSARCOMA OF THE THORAX IN A CHILD

Aims: This case illustrates the difficulties and pitfalls of diagnosis of alveolar rhabdomyosarcoma in its solid variant and in an unusual p rimary location, the mediastinum. Case details: A 9-year-old boy prese nted with a primary thoracic tumour associated with metastasis in the left sacroiliac joint, Bronchial and mediastinal biopsies showed a mal ignant neoplasm with a solid sheet-like pattern of small round cells w ith a high nuclear to cytoplasmic ratio associated with little or no f ibrosis usually evocative of a peripheral neuroectodermal tumour (PNET ) at this age, Immunohistochemical positive staining with vimentin (80 % of tumour cells), desmin (20%) and titin (30%) antibodies was sugges tive of a rhabdomyosarcoma, In addition, all neural cell adhesion mole cule (NCAM) markers tested were positive as well as MIC2, a marker for the Ewing family of sarcomas, There was no rhabdomyoid differentiatio n at ultrastructural examination, Molecular analysis with RT-PCR ampli fication of RNA isolated from the tumour demonstrated the presence of a PAX3/FKHR fusion transcript, product of a t(2;13) reciprocal translo cation, a genetic marker specific for alveolar rhabdomyosarcoma. Concl usion: The diagnostic methodology of a small round cell tumour of the child must now include immunohistochemical study and molecular biology to confirm the diagnosis of alveolar rhabdomyosarcoma, in a solid and undifferentiated variant.