Pembrolizumab in Combination With Salvage Chemotherapy for First-relapsed or Refractory Classical Hodgkin Lymphoma

This study is testing whether adding pembrolizumab — an immunotherapy drug that helps the immune system fight cancer — to standard salvage chemotherapy improves outcomes for people whose classical Hodgkin lymphoma has relapsed for the first time or did not respond to initial treatment. **You may be eligible if:** - You have classical Hodgkin lymphoma that either returned after your first treatment or never responded to first-line therapy **You may NOT be eligible if:** - You have nodular lymphocyte-predominant Hodgkin lymphoma (a different subtype) - You have a composite lymphoma (a mixed type involving more than one lymphoma type) Talk to your doctor to see if this trial is right for you.