How would you treat a young patient with good performance status who has de novo metastatic HR+ Her2+ inflammatory breast cancer with asymptomatic leptomeningeal and CNS parenchymal disease?

If her CNS parenchymal disease is low burden and amenable to SRS I would do that first. Then place an Ommaya followed by initiation of TPH plus ovarian suppression. Finally, would begin concurrent weekly IT trastuzumab 20mg with regular monitoring of CSF for clearance of cells plus follow up brain MRI. We have had some long term HER2+ LMD responders with this protocol including one of my patients going on 6 years so far. (Figura NB, et al. Breast Cancer Res Treat. 2018) If she has responded well after six cycles of taxane you can try to stop the taxane and start an AI while continuing PH.