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Evaluation of pan‐ TRK immunohistochemistry in infantile fibrosarcoma, lipofibromatosis‐like neural tumour and histological mimics

2018; Wiley; Volume: 73; Issue: 4 Linguagem: Inglês

10.1111/his.13666

1365-2559

Yin P. Hung, Christopher D.�M. Fletcher, Jason L. Hornick,

Tumors and Oncological Cases

Aims Infantile fibrosarcoma is characterised by intersecting fascicles of spindle cells and ETV 6 – NTRK 3 gene fusion in most cases. Given histological overlap with other spindle‐cell tumours, the diagnosis can be challenging and often requires molecular confirmation. A recently developed pan‐ TRK antibody shows promise for identifying tumours with NTRK fusions. The purpose of this study was to evaluate the potential diagnostic utility of pan‐ TRK immunohistochemistry for infantile fibrosarcoma. Methods and results We evaluated whole‐tissue sections from 210 cases, including 15 infantile fibrosarcomas; five each lipofibromatosis‐like neural tumour and lipofibromatosis; 10 each primitive myxoid mesenchymal tumour of infancy ( PMMTI ) and low‐grade myofibroblastic sarcoma; 15 each fibrous hamartoma of infancy ( FHI ), myofibroma/myofibromatosis and desmoid‐type fibromatosis; and 20 each low‐grade fibromyxoid sarcoma, synovial sarcoma, spindle‐cell rhabdomyosarcoma, malignant peripheral nerve sheath tumour, fibrosarcomatous dermatofibrosarcoma protuberans (F‐ DFSP ) and nodular fasciitis. Immunohistochemistry was performed using a rabbit monoclonal pan‐ TRK antibody. Immunoreactivity for pan‐ TRK was observed in all 15 (100%) infantile fibrosarcomas, including diffuse immunoreactivity (>50% of cells) in 14 (93%) cases. Pan‐ TRK was positive in all five (100%) lipofibromatosis‐like neural tumours. Of the 190 histological mimics, diffuse pan‐ TRK immunoreactivity was noted in 16 (8%) cases, including five PMMTI , five FHI (highlighting predominantly the primitive myxoid spindle‐cell components), three F‐ DFSP , one low‐grade myofibroblastic sarcoma, one myofibroma and one spindle‐cell rhabdomyosarcoma. Conclusions Diffuse pan‐ TRK immunoreactivity is a highly sensitive but not entirely specific diagnostic marker for infantile fibrosarcoma, and may be helpful in selecting patients for TRK ‐targeted therapy. As expected, lipofibromatosis‐like neural tumours, which harbour NTRK 1 fusions, also show diffuse pan‐ TRK immunoreactivity.