4. Any number of previous treatments with the exception of previous inhibitors of PD-1, PD-L1, or PD-L2. Other prior systemic therapies must have been administered at least 2 weeks before administration of pembrolizumab; the exception to this is ipilimumab which must have been administered at least 4 weeks prior to the start of pembrolizumab. Patients are not required to have had prior systemic therapy.