Case representation
A 3-year-old male child was referred with a right-sided neck swelling.
Anatomical imaging with an MRI scan at the referring center demonstrated
a mass in the right masticator space measuring 3.3.x2.7x3.2 cm involving
the medial and lateral pterygoid muscles. Review of histological
material received from the referring center, obtained from an incisional
biopsy of this mass, showed primitive mesenchymal cells with loose,
myxoid stroma, and variable degrees of skeletal muscle differentiation.
Immunohistochemistry showed strong and diffuse Desmin expression,
nuclear expression of Myogenin in fewer than 50% of tumor cells, and
nuclear expression of MyoD1 in approximately 50% of tumour cells
(Figure 1). The histological pattern was consistent with embryonal RMS.
There was no evidence of FOXO1 rearrangement by fluorescentin-situ hybridization (FISH). Stage evaluation with PET/CT and
bone marrow examination was negative for metastatic disease. The patient
was started on chemotherapy according to the ’intermediate risk’
guidelines of the institutional protocol. After the initial 9 weeks of
chemotherapy, response evaluation demonstrated tumor progression on MR
and PET/CT imaging. At this point, his chemotherapy was intensified
according to the ’high-risk’ guidelines. Since the tumor was surgically
not amenable to resection, he received focal radiotherapy (59.4Gy) for
local control, followed by consolidative adjuvant chemotherapy according
to the high-risk protocol. He was then treated with maintenance therapy
for 12 months. At the end of his chemotherapy, the tumor mass was stable
on MRI and demonstrated a complete metabolic response on PET/CT.
However, the risk of progression/relapse is extremely high.