The detection of Tel-TrkC chimeric transcripts is more specific than TrkC immunoreactivity for the diagnosis of congenital fibrosarcoma

The t(12;15)(p13;q25) translocation, a recurrent chromosomal abnormality of congenital fibrosarcoma, leads to the expression of a Tel-TrkC fusion tran script. To determine whether detection of the chimeric protein may be helpf ul far the diagnosis of congenital fibrosarcoma, immunohistochemistry was p erformed with an anti-TrkC antibody on 26 spindle cell tumours of newborn o r young children (n=19) or adults (n=7). Four out of five congenital fibros arcomas showed TrkC immunoreactivity with cytoplasmic paranuclear staining. However, TrkC immunoreactivity was not restricted to congenital fibrosarco ma and was observed in infantile myofibromatosis, congenital haemangioperic ytoma, desmoid tumour, nodular fasciitis, fibrous hamartoma, inflammatory m yofibroblastic tumour, and adult fibrosarcoma, RT-PCR analysis was performe d on nine cases, including four congenital fibrosarcomas, for which frozen material was available. Tel-TrkC transcripts were detected by RT-PCR in the four congenital fibrosarcomas analysed, but not in the five other spindle cell humours, Furthermore, several Tel-TrkC transcripts encoding for kinase isoforms of the Tel-TrkC protein were detected in congenital fibrosarcoma and may be involved in oncogenesis, The reciprocal TrkC-Tel transcript was detected in only one congenital fibrosarcoma. While the detection of a Tel- TrkC fusion transcript is a recurrent feature of congenital fibrosarcoma, T rkC immunoreactivity does not appear specific for the diagnosis of fibromat ous paediatric tumours, Copyright (C) 2000 John Whey & Sons, Ltd.