Several of these genetic alterations are considered actionable and/or associated with mechanisms of resistance against targeted therapies, such as the ALK (G1269A) mutation,17 EGFR (M766Q) mutation,18 PIK3CA E545K mutation,19 KRAS G12D mutation,20 cMET amplification,21 and HER2 amplification.22 However, there was no modification in systemic therapy to target the specific mutations detected in the CSF in this patient cohort due to the limited data available on the efficacy of these therapies in patients with LMD at the time of CSF analysis. The gene discussed is PIK3CA; the disease is Langer mesomelic dysplasia.