Chromosomal alterations in oligodendroglial tumours over multiple surgeries: is tumour progression associated with change in 1p/19q status?

Background Oligodendroglial neoplasms have morphologic and genotypic heterogeneity. Loss of heterozy- gosity (LOH) of 1p and/or 19q is associated with increased treatment responsiveness and overall survival. However, the pathogenesis of treatment-resistance is unknown. We sought to determine if tumour progression is due to a proliferating sub-population of tumour cells with intact 1p, or if recurrent tumours retain 1p/19q LOH. Methods 24 patients with oli- godendroglial neoplasms, possessing biopsy samples taken at diagnosis and at progression, were identified. 53 tumour specimens were available for LOH analysis of 1p and 19q, using PCR amplification of multiple microsatellite markers. 40 were also tested for 9p and 10q. Results At diagnosis, the median age was 34 (24-66) years, 14 were male. 19 tumours were WHO Grade II, and 5 were high grade. The most com- mon genomic status was 19q LOH (70%). 13 (54%) tumours were 1p LOH at diagnosis: of these, 12 were 19q LOH, and 1 was 19q uninformative. All 12 patients with 1p/19q LOH primary tumours had persistent co-deletion at progression. 9 (38%) tumours were 1p intact at diagnosis, and 8 remained 1p intact in the progressed tumours. There was little heteroge- neity of 9p and 10q between tumours at diagnosis and progression. Conclusion 100% of oligodendroglial tumours with 1p/19q LOH, demonstrated persistent 1p/19q LOH in the progressed tumour. Therefore, progression of these tumours is not due to a proliferating sub-population of treatment-resis- tant, 1p intact tumour cells. We propose that additional mutations contribute to this aggressive phenotype, however, 9p LOH or 10q LOH are unlikely to be involved.