1p19q codeletion

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1p19q codeletion stands for the combined loss of the short arm chromosome 1 (i.e. 1p) and the long arm of chromosome 19 (i.e. 19q) and is recognized as a genetic marker predictive of therapeutic response to both chemotherapy and combined chemoradiotherapy and overall longer survival in patients with diffuse gliomas, especially those with oligodendroglial components .

Historically, the 1p19q codeletion was present in up to 70-85% of oligodendrogliomas and 50% of oligoastrocytomas . The recent (2016) revision to the WHO classification of CNS tumors has highlighted the importance of 1p19q codeletion by making it essential for the diagnosis of oligodendroglioma (along with the IDH mutation).

In other words:

When the IDH is negative, it corresponds to a ‘wild-type’ and the tumor behaves far more aggressively, with a poor prognosis, similar to that of primary glioblastoma multiforme . This is discussed further in the article on IDH.