- Participants with known brain metastases or leptomeningeal metastases must be excluded unless they qualify for enrollment as described below because of poor prognosis and concerns regarding progressive neurologic dysfunction that would confound the evaluation of neurologic and other adverse events; participants with brain metastases are permitted if metastases have been treated and there is no magnetic resonance imaging (MRI) evidence of progression for at least 4 weeks or more after treatment is complete and within 4 weeks prior to the first dose of nivolumab administration