Chromosomal alterations in oligodendroglial tumors over multiple surgeries: Is progression associated with change in 1p/19q status?

10577 Background: There is morphologic and genotypic heterogeneity of oligodendroglial neoplasms. Tumors with loss of heterozygosity (LOH) of 1p and/or 19q are associated with increased chemo-sensitivity and survival. Despite treatment, rates of recurrence and malignant transformation are high. The pathogenesis of treatment-resistance is unknown. We aim to determine if tumour progression is associated with a proliferation of clonagens with retention of heterozygosity (ROH) of 1p, or if progressing tumours remain 1p/19q LOH. Methods: Between 1/1/2001 and 7/31/2006, 24 patients with oligodendroglial neoplasms, and possessing serial biopsies taken at diagnosis and at progression, were identified. Using PCR amplification of multiple microsatellite markers, a total of 53 tumour specimens were available for LOH analysis of 1p and 19q; 40 were also tested for 9p and 10q. Results: At diagnosis, the median age was 34 (24–66) years and 14 were male. Using the WHO criteria, 19 tumors were Grade II oligodendrogliomas or oligoastrocytomas, and 5 were high grade. The most common genomic status was 19q LOH (88%); 54% had 1p LOH. Of the 13 primary biopsies with 1p LOH, 11 had 19q LOH, 1 had 19q ROH, and 1 was 19q non-informative. A further 2 primaries were mixed 1p LOH/ROH, and 9 were 1p ROH. At progression, 10 of 11 patients with 1p/19q LOH had persistent co-deletion. The patient with 1p LOH and 19q ROH at diagnosis, had 1p/19q LOH at progression. Of the mixed 1p primaries, 1 was 1p ROH, and the other remained mixed LOH/ROH at progression. 8 of 9 primaries with 1p ROH remained 1p ROH. There was also little heterogeneity of 9p and 10q between primary and progressive tumours. Using Kaplain-Meier analysis, mean overall survival (OS) for the group was 102 (95% CI: 77–127) months. Mean progression-free survival was 52 (95% CI: 33–72) months. OS was not statistically significant between patients with 1p LOH and 1p ROH primary tumours. Conclusions: 91% of repeat biopsies of oligodendroglial tumors, demonstrated persistent 1p/19q LOH. Therefore, progression of 1p/19q LOH primary tumours is not due to a proliferating sub-group of chemo-resistant, 1p ROH clonagens. We propose that additional mutations contribute to this aggressive phenotype. No significant financial relationships to disclose.