A Phase II Study of the Combination of Pembrolizumab and ATRA Combination Treatment of Relapsed HL and B-NHL

This phase II trial is testing the combination of two drugs — pembrolizumab (an immunotherapy) and ATRA (a vitamin A derivative) — in adults with Hodgkin lymphoma or B-cell non-Hodgkin lymphoma that has come back or stopped responding to prior treatment. **You may be eligible if...** - You are 18 or older - You have Hodgkin lymphoma that has failed at least one prior treatment - You have B-cell non-Hodgkin lymphoma (such as diffuse large B-cell, follicular, mantle cell, or marginal zone lymphoma) that has failed at least two prior treatments - You have primary mediastinal large B-cell lymphoma that did not respond to first-line therapy - You have a good general fitness level (ECOG 0-2) and a life expectancy of at least 12 weeks - A tumor tissue sample from your cancer is available for testing **You may NOT be eligible if...** - You have not tried prior therapies - You have severe organ dysfunction - You are pregnant or breastfeeding - Your lymphoma does not match the eligible subtypes Talk to your doctor to see if this trial is right for you.