CDK4 and aneurysmal bone cyst: Despite a better knowledge of the molecular biology of luminal ABC and the introduction of several targeted therapies that clearly improve ET efficacy (CDK4/6i, mammalian target of rapamycin [mTOR] inhibitors, and phosphatidylinositol 3-kinase [PI3K] inhibitors), all patients who initially respond to ET become finally resistant to this treatment [2].