Management of Gliomas with Isolated 1p Deletion

Diagnostic Considerations

The National Comprehensive Cancer Network recommends that a tumor with isolated 1p deletion (without 19q codeletion) should be classified and managed as an astrocytoma, not an oligodendroglioma, because the diagnosis of oligodendroglioma requires both 1p AND 19q codeletion along with IDH mutation 1, 2, 3
True oligodendroglioma requires BOTH IDH mutation AND complete 1p/19q codeletion, as stated by the National Comprehensive Cancer Network 1, 3, 4
Isolated 1p deletion (or 19q deletion alone) without the partner chromosome loss means the tumor is NOT an oligodendroglioma, according to the National Comprehensive Cancer Network 2, 5

For Grade 2 tumors (1p deleted, 19q intact, IDH-mutant = Astrocytoma, IDH-mutant, WHO grade 2), the National Comprehensive Cancer Network recommends initial management options including wait-and-see approach for low-risk patients or radiotherapy followed by PCV chemotherapy for higher-risk patients 1, 3, 6, 7
For Grade 3 tumors (1p deleted, 19q intact, IDH-mutant = Anaplastic astrocytoma, IDH-mutant, WHO grade 3), the standard treatment is radiotherapy followed by temozolomide, as recommended by the National Comprehensive Cancer Network 1, 3, 6

The RTOG 9402 trial demonstrated that patients with 1p/19q codeletion had a significant OS benefit from PCV + RT, but patients with 1p/19q intact or only one deletion did not, as reported by the National Comprehensive Cancer Network 2, 5
The EORTC 26951 trial showed that subgroups with IDH-mutant status and 1p/19q codeletion derived the most benefit from combined therapy, as stated by the National Comprehensive Cancer Network 5

The National Comprehensive Cancer Network recommends checking ATRX status, as ATRX loss and 1p/19q codeletion are virtually mutually exclusive 4, 8
Confirming IDH mutation status is also recommended, starting with IDH1 R132H immunohistochemistry and proceeding to IDH1 codon 132 and IDH2 codon 172 sequencing if negative, as stated by the National Comprehensive Cancer Network 4, 8

For recurrent disease, the National Comprehensive Cancer Network recommends temozolomide or nitrosourea-based chemotherapy, and considering repeat surgery if feasible with multidisciplinary consultation 3, 6, 9

The National Comprehensive Cancer Network recommends levetiracetam as the first-line antiepileptic therapy due to lack of drug interactions with chemotherapy, and avoiding enzyme-inducing anticonvulsants as they interfere with chemotherapy metabolism 9