Vijayakrishna Gadi, MD, PhD: This is going to dovetail on what we were just talking about: defining these patients. How are we monitoring them? How do we define a patient who might be progressing? The big topic now is do we screen for brain metastases in patients whose baselines maybe don’t have them, but they’re on therapy? Nancy, maybe you can comment on this and about circulating tumor DNA [ctDNA] and what role that might have.

Nancy Lin, MD: In terms of extracranial imaging, we generally do CT scans as our go-to. Occasionally we’ll move to PET [positron emission tomography] scans if there’s some issue on the CT—a patient can’t tolerate IV [intravenous] contrast, there’s imaging of bone-only disease, or there are other circumstances for which we might use PET instead of a regular CT. As far as brain screening, it’s a good question. We don’t do it as standard of care, and the guidelines don’t recommend it. That’s because of a lack of evidence as opposed to evidence of no benefit, and that’s a different situation.

Through an ASCO [American Society of Clinical Oncology] CDA [Career Development Award]—is running a randomized trial of screening or no screening in patients who are starting or who are on chemotherapy for HER2 [human epidermal growth factor receptor 2]–positive disease or ER [estrogen receptor]–positive disease. Patients with triple-negative disease are also screened in this trial, but it’s not randomized. The end point is neurological functions—a quality-of-life end point, because it took a long time to think about what the right end point might be. There’s an 8-minute brain MRI-screening protocol, so it will be nice if it pans out. But there are other trials. There’s a trial in Canada that’s similar. This is a question on the minds of a lot of patients. I certainly have an extremely low threshold to order brain a MRI for my patients with HER2+ metastatic disease.

With respect to ctDNA, I’m not using it to monitor disease response. I’m not using it in a quantitative way. It’s something that Dr. Heather Parsons, as part of the STOP-HER2 trial, will be testing to see whether we can use minimal residual disease and exceptional responders to pick out patients who can stop therapy. But that’s very investigational. I do use liquid biopsies to look at alternative genetic alterations, but I don’t use them in HER2+ patients. I tend to use them in in ER+ or triple-negative patients, where you’re more likely to see something that might ultimately affect the treatment you prescribe. For HER2+ patients, I’m not using liquid biopsies in any way in clinical practice.

Transcript edited for clarity.