The CDKN2A/CEN9 probe is located on chromosome 12. A 340 Kb probe covering the CDKN2A gene region at 9p21.3 is labeled with an orange dye, and part of chromosome 9 (CEN9) is labeled with a green dye.

CDKN2A FISH probes primarily detect deletions of the 9p21 locus, a critical biomarker in cancer diagnostics. They are essential for distinguishing malignant melanoma from benign lesions and for prognostic stratification in gliomas, particularly upgrading IDH-mutant astrocytomas to WHO grade 4. This test also aids in assessing chromosomal abnormalities in bladder cancer and guiding therapy decisions in some leukemias.