How would you approach a patient with metastatic ER/PR+, HER2- breast cancer with linear leptomeningeal enhancement on MRI but negative CSF protein and cytology?

First, it is important to note that the sensitivity of CSF cytology depends on both the number of LPs and the volume of LP. For example, one LP has a sensitivity of only ~70%, while doing more than 3 LPs takes the sensitivity up to 98%. Similarly, withdrawing at least 10 ml of CSF improves sensitivi...