Successful Treatment of Recurrent Primitive Myxoid Mesenchymal Tumor of Infancy With Internal Tandem Duplication.

Primitive myxoid mesenchymal tumor of infancy (PMMTI) is a rare tumor with <20 cases reported to date. Recently PMMTI tumors have been found to harbor internal tandem duplication (ITD), the same genetic alteration detected in clear cell sarcoma of the kidney (CCSK). Complete surgical resection of PMMTI is often curative, but no standard of care has been established for unresectable tumors. We describe a female patient who presented at 13 months of age with a paraspinal mass and spinal cord compression. Histology was consistent with PMMTI, and the tumor was found to harbor ITD. The patient experienced disease recurrences after multiple surgical resections. After failing to respond to vincristine and actinomycin therapy, the patient demonstrated a nearly complete response to a doxorubicin-containing chemotherapy regimen. The patient's therapy was consolidated with proton beam radiotherapy, and she has remained in remission for >12 months after the conclusion of therapy. This case confirms ITD as a key finding in PMMTI. The therapeutic approach described here is similar to that used for CCSK and provides a model for the treatment of PMMTI not amenable to complete surgical resection.