An observational, prospective, multicenter study to be conducted in 5 hospitals in Spain. Patients with cancer undergoing radiotherapy are malnourished or at risk of malnutrition. Due to the characteristics of their pathology or gastrointestinal disorders, the use of oligomeric nutritional formulas formulated with 100% hydrolyzed whey lactoprotein and a high MCT content is recommended as part of routine clinical practice. Patients will be followed for 12 weeks, with three visits: a baseline visit upon inclusion in the study, after 6 weeks and a final visit 12 weeks after the nutritional treatment starts.

The prevalence of malnutrition is high in cancer patients: about 80% of patients will suffer from malnutrition at some point, and it is the cause of 10-20% of deaths in this type of patient.

To address malnutrition in these patients, international clinical guidelines recommend periodically reviewing their nutritional status and supplementing with oral nutrition formulas (ONS) when they are unable to meet their nutritional needs from their usual diet.

The ONSs have a nutrient composition designed to meet the specific needs of the patient, but there are pathologies, types of tumours and treatments, such as radiotherapy, chemotherapy, immunotherapy and others that can alter the digestion process, making it difficult for the gastrointestinal tract to utilise nutrients. Patients with these pathologies often cannot tolerate polymeric SNO formulations and require oligomeric peptide-based diet (PBD) formulations.

PBDs contain hydrolysed proteins in the form of peptides and medium-chain triglycerides (MCTs), which are more easily assimilated, helping patients to reduce weight loss and improve overall nutritional status. In addition, they contain hydrolysed serum lactoprotein with high biological quality that stimulates the formation of muscle tissue, minimising cachexia.

Radio/chemotherapy/immunotherapy treatment has negative effects on the nutritional and functional status of cancer patients, which also makes them more susceptible to the toxicities of cancer treatments and clinical complications. It has been shown that these patients tolerate PBD formulas well and even reduce their baseline intestinal symptoms, which facilitates compliance with nutritional treatment. However, adherence to these treatments remains a challenge as it is not always optimal, resulting in the non-achievement of the potential benefits.

The main objective of the study is to evaluate the effects of a hypercaloric SNO, with 100% hydrolysed serum lactoprotein and high MCT intake, in cancer patients undergoing radiotherapy, malnourished or at risk of malnutrition, in terms of improving the patient's nutritional status after 12 weeks of treatment.

Inclusion Criteria:

• Patients of legal age (≥18 years).
• Oncology patients (with head and neck, lung or rectal cancer) undergoing or about to start radiotherapy treatment. Patients with oesophageal cancer will also be included, as long as the patient is not undergoing PEG.
• Patients who are malnourished or at risk of malnutrition according to GLIM criteria.
• Patients requiring supplementation with an oligomeric formula with 100% hydrolysed serum lactoprotein and high MCT intake due to gastrointestinal disturbances (either maldigestion or maldigestion, malabsorption or dysmotility) intolerance to polymeric formulations or any other reason as considered by the physician.
• Patients who, at the discretion of the investigator, have the ability to answer the questionnaires and follow the procedures detailed in the protocol.
• Patients who give written informed consent to participate.

Exclusion Criteria:

• Patients with galactosemia, allergies and/or intolerances to lactose or any of the compounds of the formula.
• Patients receiving nutritional support other than that of the study characteristics or who have received it during the last month. It will be accepted in patients who, being on a polymeric SNO, are advised to change to the oligomeric formula under study, due to gastrointestinal alterations, intolerances or any other reason considered by the doctor.
• Patients who have undergone surgery in the last three months.
• Patients who have received Enteral Nutrition in the last 3 months for SNG/SNJ/PEG.
• Pregnant or lactating women.
• Patients with advanced renal or hepatic disease (with creatinine clearance less than 45 ml/min or CP=C).
• Patients with advanced neoplastic disease with life expectancy <3 months.

Oncological patients undergoing radiotherapy, who present malnutrition or risk of malnutrition and due to the characteristics of the pathology or gastrointestinal alterations, the use of oligolimeric nutritional formulas formulated with 100% hydrolyzed serum lactoprotein and high MCT content is recommended within the usual clinical practice.