Targeted next-generation sequencing demonstrated amplification of multiple genes located at 12q12-q15, including MDM2, CDK4, DDIT3, and CLL1, supporting diagnostic revision to a borderline/low-grade malignant mesenchymal neoplasm.<h4>Conclusion</h4>This case highlights that skull-based lesions initially diagnosed as ABC may recur with significant dural destruction and intradural extension, and may demonstrate aggressive neoplastic evolution. The gene discussed is CDK4; the disease is aneurysmal bone cyst.