ERBB2 and breast carcinoma: Recently, quantifying circulating tumor cells in the CSF using CellSearch showed promising results as a quantitative measure of LMD treatment response to pCSI.3 In addition, HER2-positive LMD breast cancer patients demonstrated an improved OS of 10 months when treated with intrathecal anti-HER2-targeted therapy.23 These data highlight the feasibility and utility of using CSF analysis to evaluate targetable mutations and quantifying circulating CSF tumor cells to measure therapy response in patients with aNSCLC.