A drug previously approved for adults with certain types of lymphoma or leukemia has become the first FDA approved medication for chronic graft-vs-host disease (GVHD). Ibrutinib, marketed as Imbruvica, inhibits Bruton tyrosine kinase, a protein that plays a role in the survival and spread of malignant B cells. The medication is indicated for adults who develop chronic GVHD after a hematopoietic stem cell transplant but don’t respond to systemic therapy. An estimated 30% to 70% of patients who undergo these transplants subsequently develop chronic GVHD.