PMC10393313_01
Pre-operative MRI images of the left leg showing a large lobulated invasive soft tissue mass lesion of 3.5 x 5 x 6 cm size in the upper and mid-leg involving postero-medial compartment with anterior displacement of the tibia with its bowing without any abnormal marrow signal change. Mass is hypointense on T1WI and heterogeneously hyperintense on T2WI. Mass is mainly involving the muscular structures with evidence of neuro-vascular encasement.
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figure1
The mass was encasing the neurovascular bundle of the left leg (Figure 1).
PMC10393313_02
Pathological images from the resected tumour specimen. (a): Haematoxylin-eosin staining at 10x magnification. (b): Haematoxylin-eosin staining at 20x magnification. (c): Negative IHC for desmin. (d): Negative IHC for CD34.
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figure2
Histopathology and IHC was consistent with the diagnosis of IFS (Figure 2).
MRI scan images of the left leg showing local recurrence after wide local resection and 17 cycles of VAC-based chemotherapy.
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figure3
A repeat MRI scan of the left leg was suggestive of a residual tumour (Figure 3).
FISH on interphase cell showed evidence of ETV6 translocation/ rearrangement {ETV6-NTRK3: t(12;15) (p13;q25)}.
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figure4
A histopathology review and fluorescent-in-situ hybridisation (FISH) were done on the tumour sample which showed the evidence of ETV6-NTRK3: t(12;15) (p13;q25) translocation/rearrangement (Figure 4).
Pre-chemotherapy; (a): axial T2W (fat saturated) and (b): contrast-enhanced T1W (fat-saturated) MRI images showing Ill-defined homogenously enhancing mass lesion in the Interosseous space (arrow) causing erosion of tibia and fibula. (c, d): Corresponding post-chemotherapy MR images showing significant reduction of the mass lesion with minimal enhancing residual soft tissue lesion at the end of 3 months of larotrectinib (Asterix) and (e, f) complete response after 8 months of therapy.
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figure5
The therapy was continued for 8 months and repeat imaging was suggestive of a radiologic complete response (Figure 5).