The goal of this clinical trial is to test the efficacy of laser photobiomodulation in adult hematologic cancer patients undergoing hematopoietic stem cell transplantation (HSCT). The main questions it aims to answer are: • Is photobiomodulation with laser in the oral cavity, compared to standard care, effective in preventing oral mucositis and functional impairments in adult patients receiving HSCT? • What is the level of patient´s acceptability of photobiomodulation with laser in the oral cavity during HSCT? Participants once a day will receive photobiomodulation (diode laser device) in their oral cavity from the first day of transplantation conditioning until third day post-transplant. Researchers will compare with usual care to see if photobiomodulation helps preventing oral mucositis and functional impairment.