Do you wait to treat small asymptomatic brain metastases until they reach a certain size?

For example a 1 or 2 mm brain metastasis? Would you consider waiting for these to enlarge slightly for reasons such as more certainty they are real, less normal brain to be treated, and additional lesions to declare themselves?

4 Answers

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Radiation Oncology · University of Wisconsin Hospital & Clinics

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I typically treat all lesions on MRI that are found to be concerning for brain metastases. This is after a discussion with our neuroradiologist colleagues. If there is uncertainty that a small lesion may not be a brain metastasis, then I will elect to follow with a surveillance MRI and treat in the future if there are signs of growth. Following uncertain 1-2 mm lesions with a 2-3 months brain MRI is safe strategy.

For patients with actionable genomic alterations (EGFR, ALK, etc) with many (too many for SRS) very small asymptomatic brain metastases, I recommend CNS penetrating tyrosine kinase inhibitors over whole brain irradiation. I reserve CNS directed radiation for when there is CNS progression. This approach allows us to avoid toxicities associated with upfront whole brain irradiation. For these patients with limited number of lesions, I recommend SRS upfront followed by TKI, as SRS gives the best local control.

The rationale to treat small lesions early is to maintain CNS control. Smaller lesions have a better local control rate than larger lesions. Wolf et al., PMID 28298015 have found that local control after SRS reaches 100% for intracranial metastases less than 100 mm3 in volume or 6 mm in diameter.

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Neurosurgery · Yale

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At our GK institution, treating these small lesions depends on the clinical scenario.

If all the lesions are small and this is a question of new diagnosis of brain mets, then observation with serial imaging is probably best.

If a patient with prior brain mets and only small lesions found on surveillance imaging that are not clearly mets, then serial imaging also makes sense.

If a patient with prior brain mets and lesions clearly looks like mets, then management depends on systemic therapy options. If switching systemic therapy and therapy options are CNS-penetrant, then continued imaging surveillance ok. If systemic therapy is not CNS-penetrant, then we would suggest proceeding with non-urgent treatment planning.

If small lesions are found in addition to larger lesions already planned for treatment, then we proceed with treating anything that looks like a metastasis.

If the patient is on a clinical trial that requires all brain mets to be treated with a washout period, then definitely proceed with treatment.

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Radiation Oncology · University of Florida

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Radiation Oncology · University of Arkansas for Medical Sciences

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There is another consideration that I use, and that is the location of such a small asymptomatic target. Because radiosurgery has a minimum spot size, the conformality ratio for very small lesions is high, meaning we take a divot of normal surrounding tissue that can be significantly larger than the tumor itself. You can do this safely in most parts of the brain, but if the tiny lesion is in a critical location (e.g., brainstem), I use very short-interval imaging, about 4 weeks, and treat when the tumor approximates the size of the smallest radiosurgical "spot" at 4-5 mm.