Pembrolizumab and Vorinostat in Patients With Relapsed or Refractory DLBCL, FCL or HL.

Inclusion Criteria: * Have a histologically confirmed diagnosis of follicular lymphoma, diffuse large B-cell lymphoma, or classical Hodgkin lymphoma according to the World Health Organization (WHO) classification, with hematopathology review at the participating institution * FL: grade 1, 2, 3A, or 3B are eligible * DBLCL: transformed indolent lymphomas (TIL), primary mediastinal large B-cell lymphoma (PMBCL), and aggressive B-cell lymphoma unclassified (BCL-U) are eligible * HL: all classical HL subtypes are eligible except for nodular lymphocyte predominant Hodgkin lymphoma, which is excluded * Patients with HL or DLBCL must refuse or not be candidates for curative autologous stem cell transplantation * Have relapsed or refractory disease after at least 1 prior regimen, including: * Recurrence of disease after a documented complete response (CR) * Progression of disease after a partial response (PR) to the prior regimen * Partial response (PR), stable disease (SD) or progressive disease (PD) at the completion of the prior treatment regimen; if a patient has PR to prior regimen without PD, there must be biopsy-proven residual disease that is measurable * Documented informed consent of the participant or legally authorized representative * Have measurable disease by computed tomography (CT) or positron emission tomography (PET) scan, with one or more sites of disease \>= 1.5 cm in longest dimension * Be willing to provide tissue from a newly obtained core or ex…