Polysomy of Chromosomes 1 and/or 19 Is Common and Associated With Less Favorable Clinical Outcome in Oligodendrogliomas

It is well established that the combined del(1)(p36) and del(19)(q13) is a positive prognostic molecular event in oligodendroglial tumors. However, very little is known about the frequency or impact of polysomy status for chromosomes 1/19. We examined 84consecutive pure oligodendrogliomas (68 World Health Organization [WHO] grade II and 16 WHO grade III) and analyzed them for del(1)(p36) and del(19)(q13) by fluorescent in situ hybridization. Polysomy status was recorded with accompanying deletion status, WHO grade, recurrence-free survival, and overall survival. Codeletion of 1p/19q was detected in 48% of cases and correlated with superior patient survival (p < 0.01), as expected. Of 84 cases, 36 (43%) showed polysomy of chromosome 1, 30 (36%) demonstrated polysomy of chromosome 19, and 28 (33%) had copolysomies of chromosomes 1/19. The presence of polysomy of either/or both chromosomes, regardless of deletion status, correlated with younger patient age at initial diagnosis (p < 0.01). Combined polysomy was associated with higher histologic tumor grade (p = 0.04) and conferred poor survival likelihood (p = 0.03). We conclude that polysomy of 1 and/or 19 is a relatively frequent occurrence in oligodendrogliomas and usually confers an unfavorable outcome.