Alveolar rhabdomyosarcoma masquerading as embryonal subtype: the value of modern molecular diagnostic testing.

A 3-year-old child presented with a history of conjunctivitis in her OS. She had hyperglobus of the OS and a palpable mass in the left inferior orbit. An urgent MRI revealed an enhancing mass in the left orbit. The patient underwent an incisional biopsy with pathologic assessment most consistent with embryonal rhabdomyosarcoma. However, subsequent molecular genetic testing of the biopsy specimen was positive for the PAX3/PAX7-FKHR chimeric gene, indicating the tumor was actually an alveolar rhabdomyosarcoma. The patient received a more intensive chemotherapy regimen and also was treated with proton-beam radiotherapy. After chemotherapy and proton irradiation, the patient's tumor shrank considerably, and she remained in remission at over 3 years of follow up. This patient illustrates the new tools at the disposal of the orbital specialist including molecular genetic testing and proton-beam irradiation to diagnose and treat orbital rhabdomyosarcoma.