When cancer spreads to the brain, can cerebrospinal fluid (CSF) testing provide answers that blood testing may not?

Dr. Daniel Chan, Medical Oncologist at Icon Cancer Centre Mount Elizabeth, discusses the growing role of cerebrospinal fluid (CSF) testing in guiding treatment decisions for patients with brain metastases and leptomeningeal disease.

Drawing on a real patient case and the latest NCCN Guidelines, he explains how CSF testing can help identify actionable genetic changes when blood testing or tissue biopsy may not be feasible.

Video Transcript: When cancer spreads to the brain, obtaining molecular insights can be challenging. Could cerebrospinal fluid (CSF) provide additional answers?

We are now seeing, with the advent of all these targeted therapies, that many patients, especially lung cancer patients on targeted therapy, they are often having final battles in the brain. Extracranially, it is all well-controlled, but they have brain metastases.

I'm Dr. Daniel Chan. I’m a medical oncologist. I graduated in the year 2000 and have been practicing as an accredited medical oncologist for the past 16 years.

How can CSF testing help?

It is not infrequent that the only site of metastasis is in the brain or in the cerebrospinal fluid only, which is leptomeningeal metastasis. To surgically biopsy this, it is pretty major.

Taking a blood sample, hoping that a blood sample can reflect what's in the cerebrospinal fluid or brain, has not really borne out in the literature.

I think this is where I think advances have helped. We are now able to obtain the cerebrospinal fluid to help us figure out: Has the genetic makeup of the cancer changed in this leptomeningeal disease? Is the current drug still effective?

Can you share a patient example?

It’s actually a case of a primary brain tumor. The patient had a BRAF V600E mutation, and this was picked up on the cerebrospinal fluid.

In the past two years, the US Food and Drug Administration (FDA) has approved the use of BRAF and MEK inhibitors in combination to treat this group of tumors, and the response was very good.

What do the latest NCCN Guidelines say about CSF testing?

I was quite heartened when I looked at the NCCN Guidelines recently. They do talk about using cerebrospinal fluid to help with the evaluation, especially when it is in the brain-only or is leptomeningeal disease-only progression, to help us elucidate what the next step of treatment would be.

Any pearls to share with the community?

It's not meant to replace liquid biopsy of the blood or tumor tissue biopsy if there is an obvious high extracranial load and progression.

But there will be cases, especially when the tumor involves the brainstem and the risks are just too high, where a liquid biopsy using the cerebrospinal fluid would actually be of great help.

It is our hope that as time goes by, all these methodologies will be adopted by more and more laboratories to increase access to it and help our patients.