At least 7 days after the last dose of a biologic agent; for agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur; the duration of this interval must be discussed with the study chair Biologic (anti-neoplastic) agent: at least 7 days since the completion of therapy with a biologic agent; for agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur Biologic or investigational agent (anti-neoplastic): patient must have recovered from any acute toxicity potentially related to the agent and received their last dose of the investigational or biologic agent >= 7 days prior to study enrollment\r\n* For agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur At least 7 days must have passed after the last treatment with a biologic agent; for agents that have known adverse events occurring beyond 7 days from administration, this period must be extended beyond the time during which adverse events are known to occur; the duration of this interval must be discussed with the study chair Biologic (anti-neoplastic agent): at least 7 days after the last dose of a biologic agent; for agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur; the duration of this interval must be discussed with the study chair At least 14 days since the completion of therapy with a biologic agent; for agents that have known adverse events occurring beyond 14 days after administration, this period must be extended beyond the time during which adverse events are known to occur; these patients must be discussed with the Study Chair or Co-Chair on a case-by-case basis including any patient on a drug with a half-life of > 48 hours At least 7 days must have elapsed since the completion of therapy with a biologic agent. For biologic agents that have known adverse events occurring beyond 7 days after administration, the period prior to enrollment must be extended beyond the time during which adverse events are known to occur. Biologic agent: patient must have recovered from any toxicity potentially related to the agent and received their last dose of the biologic agent >= 7 days prior to study registration\r\n* For agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur; the duration of this interval should be discussed with the study chair\r\n* For biologic agents that have a prolonged half-life, the appropriate interval since last treatment should be discussed with the study chair prior to registration Biologic (anti-neoplastic agent): At least 7 days since the completion of therapy with a biologic agent. For agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur. The duration of this interval must be discussed with the Study Chair. Biologic or investigational agent (anti-neoplastic): Patient must have received their last dose of the investigational or biologic agent >= 7 days prior to study enrollment \r\n* For agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur; the duration must be discussed with and approved by the study chair\r\n* Monoclonal antibody treatment and/or agents with prolonged half-lives: at least three half-lives must have elapsed prior to enrollment INCLUSION CRITERIA FOR STRATUM C: Patient must have received their last dose of the investigational or biologic agent >= 7 days prior to study enrollment\r\n* For agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur; the duration must be discussed with and approved by the study chair\r\n* Monoclonal antibody treatment and/or agents with prolonged half-lives: at least three half-lives must have elapsed prior to enrollment At least 7 days must have elapsed since completion of therapy with a biologic agent; for agents that have known adverse events occurring beyond 7 days after administration, this period prior to enrollment must be extended beyond the time during which adverse events are known to occur Therapy with biologic agents (non-myelosuppressive) must have been completed >= 7 days prior to study entry; for agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur Biologic (anti-neoplastic agent): at least 14 days since the completion of therapy with a biologic agent; for agents that have known adverse events occurring beyond 14 days after administration, this period must be extended beyond the time during which adverse events are known to occur; these patients must be discussed with the Study Chair on a case-by-case basis At least 7 days must have elapsed since completion of therapy with a biologic agent; for agents that have known adverse events occurring beyond 7 days after administration, this period prior to enrollment must be extended beyond the time during which adverse events are known to occur Biologic (anti-neoplastic agent): at least 7 days must have elapsed since the completion of therapy with other biologic agents; for other biologic agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur; the duration of this interval must be discussed with the study chair Biologic (anti-neoplastic agent): At least 7 days since the completion of therapy with a biologic agent. For agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur. The duration of this interval must be discussed with the Study Chair. Biologic agent - must have recovered from any acute toxicity potentially related to the agent and received their last dose of the biologic agent > 7 days prior to study enrollment\r\n* For agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur Biologic (anti-neoplastic agent): must not have received within 7 days of entry onto this study (21 days if prior vascular endothelial growth factor (VEGF)-trap and at least 3 half-lives after last dose of a monoclonal antibody); for biologic agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur Biologic (anti-neoplastic agent): at least 7 days since the completion of therapy with a biologic agent such as steroids, retinoids; Note: for agents that have known adverse events occurring beyond 7 days after administration (i.e. monoclonal antibodies), this period must be extended beyond the time during which acute adverse events are known to occur Biologic (anti-neoplastic) agent: at least 7 days since the completion of therapy with a biologic agent or donor lymphocyte infusions (DLI); for agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur Biologic (anti-neoplastic agent): at least 7 days after the last dose of a biologic agent; for agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur; the duration of this interval must be discussed with the study chair At least 7 days since the completion of therapy with a biologic agent; for agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur; the duration of this interval must be discussed with the study chair Subject has had prior treatment with biologic antineoplastic agents less than 7 days before the first dose of lenalidomide. For agents that have known Adverse Events (AEs) occurring beyond 7 days after administration (ie, monoclonal antibodies), this period must be extended beyond the time during which acute AEs are known to occur. Patients must have received their last dose of any other biologic agent greater than 7 days prior to enrollment\r\n* For agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur and discussed with the PI Biologic (anti-neoplastic agent): at least 14 days since the completion of therapy with a biologic agent; for agents that have known adverse events occurring beyond 14 days after administration, this period must be extended beyond the time during which adverse events are known to occur; these subjects must be discussed with the study chair on a case-by-case basis At least 7 days after the last dose of a biologic agent; for agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur; the duration of this interval must be discussed with the principal investigator Biologic (anti-neoplastic) therapy: It must be at least 7 days after last does of biologic agent. For agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur. The duration of this interval must be discussed with the study chair Investigational/biologic agent: \r\n* Biologic or investigational agent (anti-neoplastic): patient must have recovered from any acute toxicity potentially related to the agent and received their last dose of the investigational or biologic agent >= 7 days prior to study registration \r\n** For agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur\r\n* Monoclonal antibody treatment and agents with known prolonged half-lives: at least three half-lives must have elapsed prior to registration; Note: a list of the half-lives of commonly used monoclonal antibodies is available on the Pediatric Brain Tumor Consortium (PBTC) webpage under Generic Forms and Templates Biologic (anti-neoplastic agent) or metronomic non-myelosuppressive chemotherapy: at least 7 days must have elapsed since the completion of therapy with a biologic agent; for agents that have known adverse events occurring beyond 7 days after administration, this period prior to enrollment must be extended beyond the time during which adverse events are known to occur RECURRENT/ PROGRESSIVE DIPG (STRATUM 1): Biologic or investigational agent (anti-neoplastic): patient must have recovered from any acute toxicity potentially related to the agent and received their last dose of the investigational or biologic agent >= 7 days prior to study enrollment \r\n* For agents that have known adverse events occurring beyond 7 days after administration, this period must be extended beyond the time during which adverse events are known to occur, and discussed with the principal investigator At least 7 days must have passed after the last treatment with a biologic agent; for agents that have known adverse events occurring beyond 7 days from administration, this period must be extended beyond the time during which adverse events are known to occur; the duration of this interval must be discussed with the study chair