Must be obtained within 14 days prior to registration for protocol therapy: Absolute neutrophil count (ANC) >= 1,500/mcLXx_NEWLINE_xXWithin 14 days of treatment initiation: Absolute neutrophil count >= 1,500/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mL within 28 days prior to registrationXx_NEWLINE_xXWithin 2 weeks prior to screening step registration and within 4 weeks prior to treatment step registration: Absolute neutrophil count >= 1,500/mcLXx_NEWLINE_xXWithin 28 days prior to registration: ANC >= 1,000/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) of >= 1,500/mL within 21 days prior to registration; patients must not have had a blood transfusion within 28 days prior to registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcl obtained within 28 days prior to sub-study registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL within 14 days prior to step 2 randomizationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL within 28 days prior to registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcL; must be obtained within 28 days prior to registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 microliter (mcL), obtained within 28 days prior to step 2 registrationXx_NEWLINE_xXWithin 14 days prior to registration: Absolute neutrophil count (ANC) >= 1,500/mclXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL within 28 days prior to registrationXx_NEWLINE_xXObtained within 28 days prior to registration: Absolute neutrophil count (ANC) >= 1,500/mclXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcl documented within 28 days prior to step 1 registrationXx_NEWLINE_xXANC > 1,500/mcl within 28 days documented prior to step 3 registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 750/mcl within 28 days prior to registrationXx_NEWLINE_xXWithin 21 days of treatment initiation:\r\nAbsolute neutrophil count (ANC) >= 1,500/mcLXx_NEWLINE_xXWithin 14 days of treatment initiation: Absolute neutrophil count (ANC) >= 1,500/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL (up to 14 days before treatment initiation)Xx_NEWLINE_xXWithin 14 days of treatment initiation:\r\nAbsolute neutrophil count (ANC) >= 1,500 /mcLXx_NEWLINE_xXWithin 10 days of treatment initiation: Absolute neutrophil count (ANC) >= 1,000 /mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1500/mcL, performed within 10 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL, performed within 14 days of treatment initiationXx_NEWLINE_xXSAFETY RUN-IN: Within 10 days of registration: Absolute neutrophil count (ANC) >= 1,500 /mcLXx_NEWLINE_xXRANDOMIZED PHASE II CLINICAL TRIAL: Within 10 days of registration: Absolute neutrophil count (ANC) >= 1,500 /mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mm^3, performed within 14 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count >= 750/mcL (documented within 28 days of registration)Xx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL, performed within 10 days of treatment initiationXx_NEWLINE_xXWithin 14 days of treatment registration: Absolute neutrophil count (ANC) >= 1,500 /mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) greater than or equal to 1,500/mcl, within 14 days prior to registration; this ANC cannot have been induced by granulocyte colony stimulating factorsXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 /mcL, performed within 14 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 /mcL within 14 days of treatment initiationXx_NEWLINE_xXMCLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcL (performed within 28 days of treatment initiation)Xx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 /mcL, performed within 28 days of study registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 750/mcL; a subject will not be excluded because of pancytopenia related to diseaseXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 /mcL, performed within 28 days of treatment initiationXx_NEWLINE_xXPerformed within 10 days of treatment initiation: Absolute neutrophil count (ANC) ? 1,500/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 /mcL, should be performed within 10 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 / ml obtained =< 14 days prior to study initiationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 /mcL, performed within 10 days of treatmentXx_NEWLINE_xXAbsolute neutrophil count (ANC) ? 1,500 /mcL within 21 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcL within 21 days of treatment initiationXx_NEWLINE_xXPerformed within 10 days of treatment initiation: absolute neutrophil count (ANC) >= 1,500 /mcLXx_NEWLINE_xXShould be performed within 30 days of treatment initiation: absolute neutrophil count (ANC) ? 1,000 /mcLXx_NEWLINE_xXWithin 28 days of cycle 1 day 1: Absolute neutrophil count (ANC)\t>= 1,000/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 /mcL (performed within 10 days of treatment initiation)Xx_NEWLINE_xXWithin 5 days prior to the start of study treatment: Absolute neutrophil count (ANC) >= 1,500 /mcL.Xx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 /mcL, performed within 14 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL, performed within 28 days of treatment initiationXx_NEWLINE_xXTo be performed within 14 days of treatment initiation: absolute neutrophil count (ANC) ? 1,500 /mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) ? 1,000 /mcL within 14 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count >= 1,500/mcL within 14 days of treatment initiationXx_NEWLINE_xXWithin 10 days of treatment initiation: Absolute neutrophil count >= 1500/mcL.Xx_NEWLINE_xXWithin 14 days of treatment initiation: Absolute neutrophil count (ANC) >= 1,500/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1.5 k/mcl, obtained within 7 days prior to first study treatmentXx_NEWLINE_xXPerformed within 10 days of treatment initiation: Absolute neutrophil count (ANC) >= 1000/mcLXx_NEWLINE_xXWithin 7 days of registration: Absolute neutrophil count (ANC) >= 1,500/mcLXx_NEWLINE_xXWithin 10 days prior to on-study date: Absolute neutrophil count (ANC) ? 1,500/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 750 /mcLXx_NEWLINE_xXObtained within 21 days of registration: absolute neutrophil count (ANC) > 1,500/mcLXx_NEWLINE_xXWithin 10 days of treatment initiation: Absolute neutrophil count (ANC) >= 1,500/mcLXx_NEWLINE_xXWithin 14 days prior to registration: Absolute neutrophil count (ANC) >= 1,000/mcl; this ANC cannot have been induced by granulocyte colony stimulating factorXx_NEWLINE_xXWithin 10 days of treatment initiation: Absolute neutrophil count (ANC) ? 1,500/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 /mcL (performed within 10 days of treatment initiation)Xx_NEWLINE_xXPerformed within 10 days of treatment initiation: Absolute neutrophil count (ANC) >= 1,500 /mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000 /mcL, performed within 10 days of treatment initiationXx_NEWLINE_xXPerformed within 7 days of treatment initiation: Absolute neutrophil count (ANC) >= 1,500/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000 /mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcL, performed within 14 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 /mcL, performed within 10 days of treatment initiationXx_NEWLINE_xXObtained within 14 days prior to enrollment: absolute neutrophil count (ANC) >= 1,000/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1500/mcL, performed within 14 days of protocol registrationXx_NEWLINE_xXPerformed within 10 days of treatment initiation: Absolute neutrophil count (ANC) >= 1,000/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL within 14 days of treatment initiationXx_NEWLINE_xXWithin 10 days of treatment initiation: Absolute neutrophil count (ANC) >= 1,500/mcLXx_NEWLINE_xXWithin 14 days of treatment initiation: Absolute neutrophil count (ANC) >= 1,500/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL, performed within 14 days of registrationXx_NEWLINE_xXPerformed within 10 days of treatment initiation: Absolute neutrophil count (ANC) >= 1,500/mcLXx_NEWLINE_xXAbsolute neutrophil count >= 1,000/mcL, assessed within 14 days prior to registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcLXx_NEWLINE_xXAbsolute neutrophil count >= 500/mcL (in the absence of growth factor support), within 14 days prior to treatmentXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 500 /mcL performed within 10 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >=1,500 /mcL (within 10-15 days of treatment initiation)Xx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcL within 16 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL within 14 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000 /mcL (performed within 10 days of treatment initiation)Xx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcLXx_NEWLINE_xXWithin 10 days of treatment initiation: Absolute neutrophil count (ANC) >= 1,500/mcLXx_NEWLINE_xXCompleted within 10 days of SBRT treatment initiation: Absolute neutrophil count (ANC) >= 1,500 /mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL within 14 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL within 14 days prior to registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000 /mcL, performed within 10 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcl; this ANC cannot have been induced or supported by granulocyte colony stimulating factorsXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcL with no growth factor support in the previous 3 weeksXx_NEWLINE_xXPerformed 28 days prior to study registration up to the first dose of study drug: absolute neutrophil count (ANC) >= 1,000 /mcLXx_NEWLINE_xXWithin 10 days of treatment initiation: Absolute neutrophil count (ANC) >= 1500/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 /mcL, performed within 10 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1500/mcL (within 28 days of treatment initiation)Xx_NEWLINE_xXPerformed within 14 days (+3 working days) of treatment initiation: Absolute neutrophil count (ANC) >= 1,500 /mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcLXx_NEWLINE_xXPerformed within 14 days of treatment initiation: Absolute neutrophil count (ANC) >= 1,500/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL except in cases of marrow infiltration by lymphomaXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcLXx_NEWLINE_xXPerformed within 28 days prior to study registration up to the first dose of study drug: Absolute neutrophil count (ANC) >= 1,500 /mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL, performed within 10 days of treatment initiationXx_NEWLINE_xXPerformed within 10 days of treatment initiation; absolute neutrophil count (ANC) ? 1,500 /mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,250/mcLXx_NEWLINE_xXRelapsed/refractory MCL: Absolute neutrophil count (ANC) >= 500/mm^3; (patients who have bone marrow infiltration by MCL are eligible if their ANC is >= 500/mm^3 [growth factor allowed]; these patients should be discussed with either the principal investigator [PI] or Co-PI of the study for final approval)Xx_NEWLINE_xXNewly diagnosed MCL: Absolute neutrophil count (ANC) > 750/mm^3; patients who have bone marrow infiltration by MCL are eligible if their ANC is equal to or > than 500Xx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1 K/mcL, with or without filgrastim (GCSF) supportXx_NEWLINE_xXELIGIBILITY CRITERIA FOR REGISTRATION: absolute neutrophil count >= 1,500/mcL (within one week of registration if patient postop, otherwise within two weeks of registration)Xx_NEWLINE_xXAbsolute neutrophil count (ANC) ? 1,000/mcL OR ? 750/mcL if neutropenia due to iBCLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL, should be performed within 10 days of treatment initiationXx_NEWLINE_xXWithin 14 days prior to registration: Absolute neutrophil count (ANC) >= 1,500/mclXx_NEWLINE_xXREGISTRATION TO TREATMENT (STEP 1): Absolute neutrophil count (ANC) >= 1,500 /mcL, within 14 days prior to first dose of pembrolizumabXx_NEWLINE_xXREGISTRATION TO TREATMENT (STEP 2): Absolute neutrophil count (ANC) >= 1,500 /mcL, within 14 days prior to first dose of pembrolizumabXx_NEWLINE_xXAbsolute neutrophil count (ANC) ? 1000 /mcL within 7 days of treatment initiationXx_NEWLINE_xXLymphocytes ? 500 / mcL within 7 days of treatment initiationXx_NEWLINE_xXAll screening labs should be performed within 14 days (+3 working days) of treatment initiation: absolute neutrophil count (ANC) >= 1,500 /mcL;Xx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 /mcL, performed within 28 days of treatment initiationXx_NEWLINE_xXWithin 10 days of treatment initiation: Absolute neutrophil count (ANC) >= 1,500/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcL without growth factors within 2 week of initiation of treatmentXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL (performed within 10 days of treatment initiation)Xx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL, OR >= 1,000/mcL if lymphomatous bone marrow involvement, performed within 10 days of treatment initiationXx_NEWLINE_xXWithin 14 days of registration: Absolute neutrophil count (ANC) >= 1,000/mcLXx_NEWLINE_xXWithin 30 days prior to treatment initiation: Absolute neutrophil count (ANC) >= 1,500/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcl obtained within 28 days prior to Step 2 re-registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcl obtained within 28 days prior to Step 2 re-registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000 /mcL if no bone marrow involvement, ANC >= 800 /mcL if documented bone marrow involvementXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcl obtained within 28 days prior to step 2 re-registrationXx_NEWLINE_xXObtained within 28 days prior to registration: Absolute neutrophil count (ANC) >= 1,500/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL; these results must be obtained within 28 days prior to registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000 cells/mcL within 42 days prior to registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 microliter (mcL) be obtained within 42 days prior to registrationXx_NEWLINE_xXCLINICAL/LABORATORY CRITERIA: Absolute neutrophil count (ANC) >= 1500/mcL; these results must be obtained within 28 days prior to registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) < 1.0 K/mcL at time of enrollmentXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL obtained within 28 days prior to registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcl obtained within 28 days prior to RE-TREATMENT registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) greater than or equal to 1,500/mcL (ANC >= 1.5 x 10^9/liter [L])Xx_NEWLINE_xXWithin 14 days prior to registration: Absolute neutrophil count (ANC) >= 1,500/mcLXx_NEWLINE_xXWithin 56 days prior to randomization: Absolute neutrophil count (ANC) >= 500 cells/mcL (0.5 x 10^9/L); hence ANC must be >= 500/mcL without myeloid growth factor supportXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mclXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mclXx_NEWLINE_xXGranulocytes (ANC) >= 1,500/mclXx_NEWLINE_xXANC >= 1,500/mcL within 14 days prior to Step 3 registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000 /mcL (performed within 10 days of treatment initiation)Xx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 /mcL, performed within 10 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL (within 14 days of treatment initiation)Xx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1.5 K/mcL, should be performed within 28 days of treatment initiation, unless otherwise indicatedXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1.0 x 10^9/L, performed within 28 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL, performed within 14 days prior to registrationXx_NEWLINE_xXWithin 14 days of treatment initiation: Absolute neutrophil count (ANC) >= 1,500 /mcLXx_NEWLINE_xXPerformed within 28 days of radiation therapy: Absolute neutrophil count (ANC) >= 1,500/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL, performed within 28 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count >= 1,500/mcL (labs should be performed within 14 days of treatment initiation)Xx_NEWLINE_xXWithin 14 days of registration: Absolute neutrophil count >= 1,000/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1.5 K/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcLXx_NEWLINE_xXMCLXx_NEWLINE_xXAbsolute neutrophil count (ANC) of at least 2000 per mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) count greater than or equal to 1,000/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) of >= 1,500/microliters within 90 days prior to registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL within 7 days of treatment initiationXx_NEWLINE_xXPerformed within 10 days of treatment initiation: Absolute neutrophil count >= 1,500/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcL, within 14 days prior to initiation of study drugXx_NEWLINE_xXAbsolute neutrophil count (ANC) > 750 cells/mclXx_NEWLINE_xXAbsolute neutrophil count (ANC) < 1.5 K/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,000/mcLXx_NEWLINE_xXPerformed within 10 days of treatment initiation: Absolute neutrophil count (ANC) >= 1500/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL within 28 days prior to registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500/mcL (performed within 10 days of treatment initiation)Xx_NEWLINE_xXObtained within 14 days prior to initiation of treatment: Absolute neutrophil count >= 1,500/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 /mcL, performed within 10 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count (ANC) < 1.0 K/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) < 1.0 K/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 /mcL, obtained =< 30 days prior to registrationXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 /mcL, performed within 10 days of treatment initiationXx_NEWLINE_xXAbsolute neutrophil count (ANC) < 1.0 K/mcLXx_NEWLINE_xXAbsolute neutrophil count (ANC) >= 1,500 /mcL, performed within 10 days of protocol enrollmentXx_NEWLINE_xX