Cytogenetic characterization of peripheral nerve sheath tumours: a report of the CHAMP study group

The findings of characteristic, sometimes pathognomonic, chromosome aberrations in several types of soft tissue tumours have not only added to our understanding of the mechanisms behind the genesis of these tumours, but have also revealed the importance of cytogenetic analysis as a diagnostic tool. For many soft tissue tumours, including peripheral nerve sheath tumours, the number of analysed cases is, however, still very low, precluding evaluations of the clinical or biological significance of different chromosomal patterns. As part of an ongoing project aiming at identifying clinical-histopathological-cytogenetic correlations among soft tissue tumours, a series of 46 benign, the vast majority of which were located in the extremities, and 20 malignant peripheral nerve sheath tumours (BPNSTs and MPNSTs, respectively) that had been successfully analysed by chromosome banding techniques were evaluated with regard to clinical, morphological, and cytogenetic features. Clonal chromosome aberrations were found in 20 BPNSTs, with abnormal karyotypes being significantly more frequent among Schwannomas than among neurofibromas. Recurrent aberrations, all of which were confined to the Schwannoma subtypes, included loss of 22q material, loss of a sex chromosome, and trisomy 7. The results show that the cytogenetic features of Schwannomas are not dependent on the site of origin. The MPNSTs, all of which had clonal chromosome aberrations, displayed complex karyotypes with numerous structural and numerical changes, except in two cases showing +7 and -22, respectively, as the sole changes. None of the recurrent imbalances was restricted to either NF1-associated or sporadic MPNST, nor was any of the imbalances significantly associated with clinical outcome. The presence of a triploid or tetraploid clone was, however, associated with grade 3 tumours and a poor prognosis. The cytogenetic findings in peripheral nerve sheath tumours show that the karyotype is a good discriminator between BPNSTs and MPNSTs, and that the pattern of aberrations among the latter may add prognostic information.