Genetic analysis of peripheral nerve sheath tumours in NF1 patients

1. Geneticanalysis of peripheralnervesheathtumoursin NF1 patients Eline Beert Catholic University of Leuven Belgium

2. Aim of the study To investigate the malignant transformation of a pre-existing (plexiform) neurofibroma towards an MPNST

3. Tumour samples in the study • (sub)cutaneous neurofibroma • isolated tumour in or under the skin • mostly asymptomatic • plexiform neurofibroma • spreads along a peripheral nerve • disfiguring, difficult to remove • atypical neurofibroma • symptomatic • painful, actively growing • increased glucose uptake (FDG-PET scan) • pathology • no mitoses ~ benign neurofibroma • BUT! hypercellular regions and atypical cells • MPNST • 8-13% life time risk • difficult to detect in early phase (→ bad prognosis if detected late) • metastasize often • five year survival of only 25%

4. Experimentalapproach • 33 NF1 patients → 52 PNSTs • 8 (sub)cutaneous neurofibromas • 7 plexiform neurofibromas • 11 atypical neurofibromas • 2 low grade MPNSTs • 2 intermediate grade MPNSTs • 22 high grade MPNSTs • genetic analysis • high resolution 244K oligonucleotide aCGH (Agilent Technologies) • CDKN2A (9p21.3) and TP53 (17p13.1) mutation analysis

5. 244K oligonucleotideaCGH • 243 504 oligonucleotide probes • 60-mer • each spotted once • overall median probe spacing of 8,9 kb • average resolution of ± 10kb

6. ResultsaCGH: Chromosome 9 • 9p21.3 → CDKN2A • neurofibromas • → no deletion • atypical neurofibromas • → 10/11 deletion • (1 homozygous) • MPNSTs: • low grade • → 2/2 deletion • (1 homozygous) • intermediate grade • → 1/2 deletion • high grade • → 15/22 deletion • (10 homozygous) neurofibroma atypical neurofibroma high grade MPNST

7. ResultsaCGH: Chromosome 17 • 17p13.1 → TP53 • neurofibromas • → no deletion • atypical neurofibromas • → no deletion • MPNSTs: • low grade • → no deletion • intermediate grade • → 1/2 deletion • high grade • → 11/22 deletion neurofibroma atypical neurofibroma high grade MPNST

8. Summary: aCGH and mutationanalysisCDKN2A and TP53

9. aCGH: most frequent deletions

10. aCGH: most frequent gains

11. aCGH: frequent amplifications

12. Conclusion • Signaling pathways possibly involved in malignant transformation • RB pathway • CDKN2A (p16INK4A), CDKN2B (p15), CDKN2C (p18) • CDK4/6 • RB1 • p53 pathway • CDKN2A (p14ARF) • MDM2 • TP53 • RTK/RAS and effector pathways • RTKs: EGFR, PDGFRA, MET • RAS/MAPK pathway • RAS/PI3K pathway (PIK3CA)

13. Conclusion • atypical neurofibromas → already multiple chromosomal aberrations • compared to high grade MPNST • smaller and less frequent deletions and duplications • in lower percentage of cells • role for inactivation of CDKN2A • no difference between atypical neurofibromas and low grade MPNSTs (! small sample size) • aCGH = a good tool to investigate genomic imbalances in tumours • if possible: detection and resection of atypical neurofibromas before further evolution

14. Acknowledgements • Prof. Dr. Eric Legius • Prof. Dr. Raf Sciot • Bruno Daniëls • Hilde Brems • Prof. Dr. Ivo De Wever • Prof. Dr. Frank Van Calenbergh • Prof. Dr. Maria Debiec-Rychter