Dexamethasone to Prevent Oral Chronic Graft-versus-Host Disease

This study will determine if a dexamethasone mouth rinse can reduce the risk of developing oral chronic graft-versus-host disease (cGVHD) in patients who have undergone a bone marrow (stem cell) transplant procedure. cGVHD is a common complication of stem cell transplantation, resulting from the donor cells attacking the transplant recipient's tissues. In oral cGVHD, the tissues in the mouth are damaged, causing painful mouth sores. Dexamethasone is a corticosteroid that is commonly used to treat inflammation. It is the only corticosteroid available that can be used as a mouth rinse. Patients 12 years of age or older who have received a stem cell transplant may be eligible to participate if they are enrolled within 70 to 90 days of their transplant. Candidates are screened with a medical history and oral exam. Participants are randomly assigned to receive either the dexamethasone rinse or a placebo (a solution that looks and tastes like the dexamethasone rinse but has no active medication). They undergo the following procedures: Treatment with the study solution. Patients rinse their mouth with the dexamethasone solution or placebo three times a day for 3 months. Clinic visits before starting treatment and at 1, 2 and 3 months after starting the study drug for the following procedures: * Oral exam (before starting treatment and at each visit). * Photographs of the mouth (before starting treatment and at 3 months). * Biopsy from inside the cheek (before starting treatment). The inside of the cheek is numbed and a small piece of tissue is removed for examination by a pathologist. * Saliva sample collection (before starting treatment). * Blood draw (before starting treatment and at each visit). * Quality-of-life questionnaires (before starting treatment and at 3 months). * Questionnaire to assess level of dry mouth and mouth pain (before starting treatment and at each visit). * Review of medications (at each visit). * ACTH stimulation test to evaluate adrenal gland function (at 3 months). Patients are given an injection of a drug called "ACTH" or "cosyntropin" which is a version of a hormone normally produced by the pituitary gland. Blood samples are drawn before the injection and at 30 and 60 minutes after the injection to measure levels of the hormone cortisol. After treatment ends, participants are contacted by telephone every month for 6 months to report any symptoms of cGVHD, and they return to the clinic at 6 months for a final evaluation.