Case Report
A 9-month-old term female presented with a one-month history of a rapidly enlarging left trapezius mass. Family history was unremarkable. Magnetic resonance imaging (MRI) showed a 3-4 cm mass involving the left trapezius and paraspinal muscles with extension into the left neural foramen at T2-3 and an epidural component at T1 (Fig 1). Staging work up was consistent with a single lesion localized to the back and spine. An excisional tumor biopsy was performed.
Pathology revealed primitive-appearing small round blue cells in a background of myxoid matrix. Immunohistochemistry showed patchy positivity for BCL-6 and NTRK, and diffuse nuclear immunoreactivity for BCOR. Tumor tissue was negative for desmin, Oscar, CD99, S100, and myogenin. Testing was negative for a NTRK gene fusion and rearrangement of ETV6. A comprehensive solid tumor molecular profiling panel was remarkable for a single variant of unknown significance at RASA1 p.Y528c. Collectively these findings were consistent with the diagnosis of PMMTI.
Given the tumor extension into the neural foramen and epidural space, complete resection of her disease was not feasible up front. She was initially treated with two cycles of vincristine (days 1,8, 15), dactinomycin (day 1) and cyclophosphamide (day 1) based on historical practice. Due to rapid, localized, progression of disease, her therapy was then changed to ifosphamide (2500mg/m2/dose; days 1-3) and doxorubicin (37.5mg/m2/dose; days 1-2), which she received for 4 cycles. Her tumor demonstrated a significant partial response, allowing for a gross total resection (GTR) of the mass. Surgical pathology demonstrated diffuse fibrosclerosis of the tumor which extended beyond the resection margins, however no signs of residual malignancy were seen. Given the previously aggressive nature of patient’s disease, good response to current therapy, and chemotherapy refractory nature of recurrent disease, she then received consolidation therapy with localized proton beam radiation (PBT) and two concurrent cycles of ifosphamide. The patient is now 34 months from initial diagnosis and continues to be in remission 27 months following the completion of her multidisciplinary therapy. Late effects include ifosphamide-induced Fanconi syndrome for which she receives oral bicarbonate supplementation.