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.