For more information regarding Bristol-Myers Squibb Clinical Trial participation, please
        visit www.BMSStudyConnect.com

        Inclusion Criteria:

          -  Pathologically confirmed PCNSL or PTL who failed or did not respond to at least 1 line
             of systemic therapy

          -  Measurable disease requirements on scans:

        PCNSL subjects should have at least one measurable extranodal brain lesion; PTL subjects
        should have at least 1 measurable extranodal lesion or nodal lesion

          -  Have tumor tissue for PD-L1 expression testing

          -  Must have a Karnofsky performance status of 70-100

        Exclusion Criteria:

          -  a) Intraocular PCNSL without evidence of brain disease b) PCNSL patients who cannot
             undergo MRI assessments c) PCNSL patients with systemic disease

          -  Patients with certain diseases such as active autoimmune disease, type I diabetes,
             hypothyroidism that needs hormone replacement, active infection, psychiatric disorder

          -  Prior malignancy active within the previous 3 years except for locally curable cancers
             that have been apparently cured, such as basal or squamous cell skin cancer,
             superficial bladder cancer, or carcinoma in situ of the prostate, cervix, or breast

          -  Prior treatment with an anti-PD-1, anti-PD-L1, anti-PD-L2, anti-CD137, or anti-CTLA-4
             antibody, or any other antibody or drug specifically targeting T-cell co-stimulation
             or checkpoint pathways

        PCNSL, and PTL subjects with brain or spinal cord lesion who have received doses of more
        than 2 mg/day of dexamethasone or equivalent within the 14 days period prior to the first
        dose of nivolumab are excluded

        Other protocol defined inclusion/exclusion criteria could apply