Genetic diagnosis of alveolar rhabdomyosarcoma in the bone marrow of a patient without evidence of primary tumor.

Alveolar rhabdomyosarcoma (ARMS) is characterized by two pathognomonic translocations, both involving the FOXO1 gene. We describe a case of a 10-year-old child with multiple lytic lesions involving all the vertebral bodies, sternum and femur and a bone marrow biopsy compatible with a small round cell neoplasia, but no evidence of a primary tumor. Interphase FISH analysis with specific probes evidenced a rearrangement involving the FOXO1 gene and RT-PCR identified the PAX7-FOXO1 fusion transcript. These data show a case of ARMS with no evidence of primary tumor presenting the PAX7-FOXO1 fusion gene.