The study is a Clinical Trial and the main objective is to Evaluate the effects of probiotics on oral complications induced by antineoplastic therapies in patients with head and neck cancer, attended at the radiotherapy service of the Catalan Institute of Oncology (ICO) Hospitalet and at the Dental Hospital of the University of Barcelona (HOUB), Faculty of Medicine and Health Sciences Bellvitge campus during the period 2022- 2024.

Research question:

Is the use of probiotics compared to placebo effective in reducing oral complications produced by antineoplastic therapies in patients with head and neck cancer attended in the radiotherapy service at the Catalan Institute of Oncology (ICO) Hospitalet and the Dental Hospital of the University of Barcelona, Faculty of Medicine and Health Sciences campus Bellvitge during the period 2022- 2024?

Study population: Patients attended at the radiotherapy service of the Catalan Institute of Oncology (ICO) Hospitalet and at the Dental Hospital of the University of Barcelona (HOUB), (Master of Dentistry in Oncology and Immunocompromised Patients) diagnosed by histological confirmation of head and neck cancer and treated in the last year.Intervention:

Patients who agree to participate in the study will be randomized to the intervention or control group. Two visits will be made, the first as a baseline measurement and the second after the end of the intervention. In the first visit they will be given the products either probiotic or placebo, with presentation of a box with 10 sachets. The probiotics contain: Lactobacillus Rhamnosus GG, Lactobacillus casei, Streptococcus thermophilus, Bifidobacterium breve, Lactobacillus acidophilus, Bifidobacterium infantis and Lactobacillus bulgaricus. 1 x 10e10 Colony Forming Units (CFU). And the placebo composed of excipients. They are gluten free. Each patient will be given 1 sachet dissolved in water, to take 2-3 minutes of mouthfuls then swallow, after brushing, once a day, for 30 days.

Background: The side effects of antineoplastic therapies of the head and neck aggravate the condition of patients resulting in a decrease in the quality of life. At oral level, they can induce the appearance of certain alterations, this predisposes to an imbalance in the oral microbiota, increasing the presence of acidogenic and cariogenic bacteria. In the oral cavity probiotics are associated with a decrease in the colony forming unit (CFU) count of cariogenic pathogens and inhibition of periodontal pathogens. In addition, they modulate the inflammatory response (humoral and cellular). For this reason, they could be considered a good alternative to modulate the oral microbiota in head and neck oncology patients. Hypothesis: The use of probiotics due to the change of the oral microbiota is associated with a beneficial effect against oral complications produced by radiotherapy, chemotherapy and surgery in patients with head and neck cancer, so that probiotic users will have a greater reduction in oral complications induced by cancer therapies compared to those who do not use probiotics. Objectives: To evaluate the effects of probiotics on oral complications induced by antineoplastic therapies in patients with head and neck cancer, attended at the radiotherapy service of the Catalan Institute of Oncology (ICO) Hospitalet and the Dental Hospital of the University of Barcelona (HOUB), Faculty of Medicine and Health Sciences Bellvitge campus during the period 2022- 2024. Methodology: Randomized Clinical Trial during the period 2022-2024. The identification of the population of interest will be patients attended in the radiotherapy service at the Catalan Institute of Oncology (ICO) Hospitalet and at the Dental Hospital of the University of Barcelona (HOUB), in the Master of Dentistry and in Oncology and Immunocompromised Patients. Data will be collected by electronic record, clinical examination, microbiological and radiographic analysis of the participants. Expected results: The use of probiotics is expected to provide a greater reduction in oral complications induced by head and neck antineoplastic therapies. Statistical analysis: Comparison of categorical variables chi-square test, numerical variables Student's test for independent samples and paired samples or Mann-Whitney U test and Wilcoxon signed-rank test. Relative risk with 95% confidence interval. An intention-to-treat analysis will be performed.

Inclusion Criteria:

• Patients over 18 years of age.
• Who give informed consent to participate in the study.
• With histologic diagnosis of head and neck cancer.
• Treated within the last year for head and neck cancer.

Exclusion Criteria:

• Patients who do not wish to participate in the study.
• Patients with osteonecrosis.
• Inability to take oral medications.
• Allergic to probiotics.
• On active antibiotic treatment or having received antibiotic treatment in the last thirty days.