HER2+ Metastatic Breast Cancer: Guidance on MRI Use After CNS Radiation


A brief review on how best to use MRI following CNS-directed radiation therapy in patients with HER2+ metastatic breast cancer.


Sara Tolaney, MD:That's really helpful. While we're talking about scan frequency, when do you think someone should get scanned after they've had radiation to the CNS? When should the time of that next scan be?

Ayal Aizer, MD: It’s a question that comes up a lot. Patients always ask, you finish radiation, but you’re not going to recommend a scan for a while. Why not just do it tomorrow? I think what we counsel our patients about is that radiation is sort of a biologic mechanism of treatment. It’s not like a laser beam that creates a hole where there once was a tumor. It takes a lot of time for the downstream effect of radiation to translate to a scan change. The NCCN [National Comprehensive Cancer Network] guidelines have typically suggested 2 to 3 months depending on the modality of radiation utilized in terms of the next MRI of the brain. We tend to do it a little bit shorter just out of concern that we really like to prevent a new tumor from causing a symptom that requires a more aggressive modality of therapy if we can.

We typically, after SRS [stereotactic radiosurgery], will get a scan about 6 weeks thereafter. With whole brain, sometimes this is a little longer, maybe 2 months or so. If a patient has rapidly progressive disease though, which thankfully is not as common in breast cancer, we will err on the shorter side. Sometimes we get a scan in a month. Some of our patients have smoldering disease, and we know that we're just radiating to prevent further growth, but it doesn't have to be now. It could be a while from now. With some of those patients, we might radiate and then get a scan in 3 months because their disease trajectory has told us that they just don't need that frequent of a scan. We tend to personalize it to some extent. We're often involved, as you all mentioned, when a patient starts a new drug. In some of those patients, if we're leaving tumors untreated, especially if we don't have a short leash, meaning the disease has bulk, there's edema, and they're on the verge of symptoms. We might get a scan in just a few weeks, like 3 weeks after, just to make sure that they're not tipping over to the edge of progression that would lead more of an acute decline. So, that's outside of the realm of radiation, but sometimes, when we're managing patients who are getting a drug alone, but their disease has propensity to cause decline, if it grows, we'd get a frequent scan in those patients.

Sara Tolaney, MD:Well, that's helpful because you're right. It does cover up a lot in medical oncology and radiation oncology when we're trying to coordinate stances. We're always going back and forth about when should that next one be, so that's very helpful to put it into perspective.

Transcript edited for clarity.

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