This randomized clinical trial aims to compare the efficacy of laser therapy and ozone therapy in the treatment of oral mucositis in adult cancer patients undergoing chemotherapy or radiotherapy, particularly those with head and neck tumors or hematologic malignancies. Oral mucositis is a frequent and debilitating complication of cancer treatment, characterized by painful ulcerations that impair nutrition, speech, and oral hygiene, often requiring opioid analgesics and supportive care. Forty eligible patients will be randomly assigned to two parallel groups. The trial group will receive high-power diode laser therapy using a flat-top handpiece at 660 nm wavelength, following a standardized photobiomodulation protocol. The control group will be treated with medical ozone gas administered via an intraoral device, using a standardized ozone therapy protocol. Both treatments will be applied once daily over five consecutive days. Patients will be followed up at 15 and 30 days after treatment initiation. The primary outcome is the reduction in mucositis severity, measured using the World Health Organization (WHO) Oral Toxicity Scale. Secondary outcomes include pain intensity assessed with the Visual Analogue Scale (VAS), and quality of life evaluated through the Oral Mucositis Weekly Questionnaire - Head and Neck (OMWQ-HN). The study seeks to determine whether laser therapy offers superior clinical benefits compared to ozone therapy in reducing lesion severity, alleviating pain, and improving patient well-being during cancer treatment.