The activities in the study hospital were seriously impacted by the medical care of COVID patients, affecting the medical management protocol of the study population. This situation does not allow to continue with the recruitment of patients.

Health-related Quality of Life (QoL) is a multidimensional construct that allows us to know the patient's perception of well-being, and how this perception is related to their illness and treatment. In clinical research, especially clinical trials, the QoL measurement has become an important element to evaluate. In patients with Head and Neck Squamous Cell Carcinoma (HNSCC), low QoL is associated with Malnutrition (MN), and Cancer Cachexia (CC) is a principal component in its multifactorial etiology. The exacerbated hypercatabolic state of CC is caused by the increase of pro-inflammatory cytokines, Reactive Oxygen Species (ROS), and other catabolic mediators. The clinical manifestation of CC is a continuous decrease in muscle mass (with or without loss of fat mass), which is not entirely reversible with nutritional support and which leads to the functional deterioration of patients. Due to CC, the patients with HNSCC who receive total enteral nutritional support have difficulties in maintaining an optimal nutritional status, and this situation is more frequent during RadioTherapy (RT). An immune-modulator nutrient, Omega-3 fatty acids (O3) have shown efficacy in improving the nutritional and inflammatory parameters of patients with HNSCC; however, little is known about their impact on patients' QoL and Functionality (Fx). Therefore, this clinical trial is proposed to provide information about the usefulness of O3 for improving the Fx and QoL of patients with HNSCC receiving total enteral nutrition during RT.

• Objective: To determine the effect of the daily addition of five mL of an O3 highly concentrated substance (EicosaPentaenoic Acid - EPA: 2.25 g and DocosaHexaenoic Acid - DHA: 1.08 g), to the standard enteral nutrition diet during RT (5-7 weeks), on the Quality of Life (QoL) and Functionality (Fx) of patients with HNSCC.
• Methods: Randomized, double-blinded, controlled clinical trial. Patients with HNSCC (ages ranging from 18-80 years) who will receive total enteral nutrition support through percutaneous endoscopic gastrostomy and RT for the first time will be invited to participate in the study. Exclusion criteria are fish allergy, anticoagulant consumption, any supplement consumption 6 months prior to the experiment, any contraindication to the performance of the body composition analysis using bioelectrical impedance (Bioelectrical Impedance Analysis, BIA) (cardiac pacemaker, any metallic prosthesis, inability to stand, severe edema), or the presence of the mal-absorption syndrome, two or more cancer types, organ dysfunction, immune diseases, or any hospitalization during the 20 days prior to extraction of the blood sample. Patients with the consumption of any other nutritional supplement or diagnosed with any other cancer during the treatment period, or with insufficient or incorrectly processed blood-serum samples will be eliminated. After expressing their willingness to participate via the signing of the informed consent document, 86 patients with HNSCC will be allocated into two groups: The O3 Group will have the addition of 5 mL of an O3 highly concentrated substance containing 2.25 g of EPA and 1.08 g of DHA to the standard enteral diet during RT (5-7 weeks), and the Placebo or Control Group will have the addition of 5 mL of a placebo (pigmented and flavored corn oil) in a similar manner. All patients will be seen every 4 weeks at the Nutrition Support Service for nutritional assessment and counseling, and to receive the enteral nutrition containers (standard polymeric diet). On the same day, a Research Assistant (who will be blinded) will provide the supplements or the placebo. The patients' sociodemographic and clinical information, body composition, albumin, hemoglobin, C-reactive protein, tumor cachexia-related cytokines: IL (Interleukin) 1a, IL-1b, IL-6, IL-8, IFNγ (Interferon gamma), TGF-β (transforming growth factor beta), and TNF-α (Tumor necrosis factor alpha); and responses for the European Organisation for Research and Treatment of Cancer Quality of Life C-30 (EORTC-QLQ-C30) with the Head and Neck Cancer module (EORTC-QLQ-H&N35) questionnaires will be collected at the beginning of RT, at the end of RT, and 12 weeks after starting RT. Statistical analysis includes descriptive statistics, inference statistics (Student t-test, Mann-Whitney test, one-way ANOVA with Bonferroni correction, Kruskal-Wallis with Dunn's non-parametric test), and the Cox regression; an intention-to-treat analysis will be performed.

Inclusion Criteria:

• Head and Neck Squamous Cell Carcinoma (HNSCC) confirmed by histologic
• Eligible for receiving total enteral nutrition support through percutaneous endoscopic gastrostomy for the first time
• Eligible for receiving RadioTherapy (RT) for the first time

Exclusion Criteria:

• Allergy to fish
• Consumption of anticoagulants
• Consumption of any supplement 6 months prior to the experiment
• Any contraindication to the performance of the Bioelectrical Impedance Analysis (BIA) (cardiac pacemaker, any metallic prosthesis, inability to stand, severe edema)
• Mal-absorption syndrome
• Two or more cancer types
• Organ dysfunction
• Immune diseases
• Any hospitalization during the 20 days prior to extraction of the blood sample