What is your surveillance strategy in patients with brain metastases who are getting systemic therapy?

Generally, I’d consider a repeat MRI every 2-3 months, earlier if warranted. Assuming no evidence of disease progression for 1 or 2 years, I’d consider every 3-6 months.

I would agree that every 3 months is reasonable. These are patients who could have a long/deep response, so would continue to monitor for years out.

As far as what triggers to treat, I will be interested to see what others would say, but I have a low threshold to treat once I see progression in a ...

I presume that the question is talking about patients with brain metastases treated with IT alone (meaning no history of radiation). This has been evaluated in Melanoma (best response with ~50-55% ORR with Ipi/Nivo here: Tawbi et al., PMID 30134131) and here (Long et al., ASCO Annual Meeting 2021), ...