The 1p (1p36/1q25) probe is located on chromosome 1. A 400 Kb probe covering the 1p36 gene region is labeled with an orange dye, and A 620 Kb probe covering the 1q25 gene region is labeled with a green dye. The 19q (19p13/19q13) probe is located on chromosome 19, A 500 Kb probe covering the 19p13 gene region is labeled with an orange dye, and A 400 Kb probe covering the 19q13 gene region is labeled with a green dye.

NCCN guidelines: High-risk low-grade gliomas require radiochemotherapy. Low-risk features include oligodendroglial histology, age <40, and 1p/19q codeletion with IDH mutation.

1p/19q codeletion frequency: 80-90% in grade II oligodendrogliomas, 50-70% in grade III, decreasing in mixed tumors. Codeletion confers alkylating agent sensitivity and better prognosis compared to single/no deletions.

Non-deleted cases show higher pseudoprogression rates. 2016 WHO classification requires IDH mutation plus 1p/19q codeletion for oligodendroglial diagnosis. 1p/19q deletions also found in glioblastoma and other CNS tumors.