[1504] Repeat Molecular Testing in Gliomas: A Retrospective Study of 53 Patients

D Mahajan, RA Prayson. Cleveland Clinic Foundation, Cleveland, OH

Background: Molecular testing for deletions on chromosomes 1p and 19q and for EGFR amplification has implications for the clinical management of certain glial tumors. The value of repeat testing in patients with multiple resections is unclear. The purpose of this study is to add to previously reported data assessing for evidence of molecular changes in gliomas which have undergone repeat testing.
Design: 53 patients (31 males; age mean 45.4 years) who had repeat molecular testing on specimens from two different resections for chromosome 1p deletion, chromosome 19q deletion and/or EGFR amplification by fluorescent in situ hybridization (FISH) were studied.
Results: Original diagnoses included 27 diffuse fibrillary astrocytomas (11 low grade, 3 anaplastic and 13 GBM), 16 oligodendrogliomas (11 low grade and 5 anaplastic), 6 mixed gliomas (4 low grade and 2 anaplastic) and 4 gliomas not otherwise specified. Nine tumors upgraded during the interval between the initial and the subsequent resection (4 astrocytomas, 2 oligodendrogliomas and 3 mixed gliomas).Paired results for 1p evaluation demonstrated a change in the profile from intact to loss in 1/50 patients (2%); the tumor upgraded from a low grade to anaplastic mixed glioma on the subsequent resection. Paired results for 19q evaluation demonstrated a change in profile in 4 of 41 patients (9.7%). Two of these tumors diagnosed as GBM on the initial and subsequent resections changed profile from 19q loss to intact. The remaining 2 tumors (1 astrocytoma and 1 mixed glioma) were initially 19q intact and changed to loss on the subsequent resection. The mixed glioma upgraded to anaplastic mixed glioma on the subsequent resection. There was no change in the EGFR expression in any of the patients tested (N= 34; 28 with no amplification, 6 with amplification). There was no change in the clinical management based on the repeated molecular tests in patients with discrepant repeat results.
Conclusions: There was only rare evidence of profile change in 1p and 19 q status (5/53 tumors) and no change in the EGFR amplification status with repeated testing. None of the tumors with change in molecular status were oligodendrogliomas. There appears to be no indication for repeat 1p/19q or EGFR FISH testing in gliomas at the time of repeat biopsy or resection.
Category: Neuropathology

Tuesday, March 10, 2009 9:30 AM

Poster Session III # 193, Tuesday Morning