Definition

The term "oncological diseases" encompasses multifactorial malignant transformations of cells. The group of affected patients is highly heterogeneous, including individuals at different stages and phases of the disease, as well as with various comorbidities and therapies. Malnutrition is common among oncology patients and contributes to nutrition-related mortality of around 20% ^[1-3]. Malnutrition can be influenced by the tumor itself and/or by treatment measures. Therefore, early and appropriate nutritional therapy must be integrated into multimodal oncology treatment concepts.

Impact on Metabolism and Nutritional Status

A combination of many factors leads to anorexia, weight loss (cachexia), hypermetabolism, and decreased anabolic stimuli (e.g., physical activity) ^[1-3]. The anorexia-cachexia syndrome is characterized by a catabolic metabolic state with disturbed neuro-humoral regulation based on a chronic inflammatory condition. Changes occur particularly in energy metabolism, as well as in carbohydrate, fat, and protein metabolism. These alterations resemble insulin resistance and result in a negative fat and protein balance. Due to these metabolic changes, tumor-associated malnutrition is often only partially reversible. The deterioration of nutritional status is independently associated with a poorer prognosis, increased treatment toxicity (interruptions or discontinuations), and reduced quality of life ^{[1, 4, 5]}.

Nährstoffbedarf von onkologischen Patient:innen. KG = Körpergewicht; d = Tag

Goals of Nutritional Therapy

• Maintain or improve nutritional status and physical function
• Prevent malnutrition or nutrient deficiencies
• Increase/optimize food intake
• Reduce systemic inflammation and hypermetabolic stress

Early nutritional therapy is essential for maintaining or improving nutritional status. Nutritional screening (e.g., Nutritional Risk Screening: NRS 2002 or PG-SGA) should be conducted as early as possible (at diagnosis, upon new clinical developments such as tumor progression, or initiation of a new therapy) and at least twice a year to identify malnourished patients. Each institution should implement defined standards for malnutrition assessment. Interdisciplinary workflows, responsibilities, and quality controls should be clearly defined and documented in protocols/algorithms. Patients undergoing curative or palliative procedures should be treated according to the ERAS (Enhanced Recovery After Surgery) concept (see details below).

Energy and protein needs should, whenever possible, be met through oral nutrition. If less than 75% of nutritional requirements are met through fortified foods, snacks, or oral nutritional supplements, supplementary enteral nutrition should be initiated within 5 days. Complementary parenteral nutrition is indicated if less than 75% of requirements are met through oral and/or enteral nutrition over a period of 10 days. The type of nutritional therapy should be tailored to the patient's condition, appetite, cancer type and stage, and treatment measures, based on therapy duration and goals. For surgical oncology patients with a risk of malnutrition or manifest malnutrition, outpatient nutritional therapy is recommended. Theoretical concerns that nutrients "feed the tumor" are not supported by clinical evidence, and nutritional intake should not be reduced ^[1-3].

Oral Nutrition

A protein- and energy-enriched diet helps improve nutritional status. Nutritional counseling should be integrated at the beginning of therapy to address nutrition-related symptoms and optimize food intake. Key elements of nutritional counseling include: (i) explaining the reasons and goals of nutritional recommendations and (ii) motivating patients to implement them ^[1-3].

Practical Tips, if Indicated

• Taste disturbances: Address individual preferences. Discuss menu options and suggest alternatives. Offer neutrally flavored oral nutritional supplements.
• Aversion to meat: Recommend vegetarian alternatives.
• Loss of appetite: Offer enriched meals (e.g., soups, frappés, Bircher muesli) from the menu system. Provide foods for self-enrichment, such as butter, whipped cream, or extra sauce. Serve smaller portions more frequently throughout the day. (Enrichment Schema PDF)
• Sensitivity to smells: Minimize food odors by ventilating well; if necessary, replace warm meals with cold options.
• Dry mouth: Stimulate saliva production with chewing gum or candies. Adjust food texture (e.g., blended, finely chopped, or with extra sauce). Recommend suitable mouth sprays for moisture. Ensure adequate fluid intake.
• Immunonutrition: Recommended for perioperative care in patients with upper gastrointestinal tract tumors. Immunonutrition involves liquid oral or enteral supplements with specific nutrients, although the function of individual components remains to be clarified.

Enteral Nutrition

Enteral nutrition (possibly home-based) helps maintain nutritional status when patients are unable to consume enough orally. This applies to oncology patients with impaired oral intake or issues with food transport in the upper gastrointestinal tract (e.g., obstructive ENT/thoracic tumors). Two recommended options for enteral nutrition include nasal tubes (nasogastric, nasojejunal) and percutaneous tubes (PEG, PRG, PEG/J, Witzel fistula, button). The choice of tube should be based on a risk-benefit analysis that considers the patient's individual situation and needs. Patients often prefer PEG tubes over nasal tubes. Before placing a PEG tube, tolerance for enteral feeding should be tested using a nasojejunal tube when appropriate.

During enteral nutrition, swallowing screenings and, if necessary, appropriate therapy are recommended. It is important to educate and motivate patients to maintain swallowing function through appropriate exercises.

Parenteral Nutrition

Parenteral nutrition (possibly home-based) is used when oral and/or enteral nutrition cannot adequately meet energy and protein needs. It can maintain or improve nutritional status in cases of severe intestinal failure. Typical indications include severe mucositis, persistent vomiting, ileus, severe malabsorption, prolonged diarrhea, symptomatic gastrointestinal graft-versus-host disease, radiation enteritis, chronic obstruction, short bowel syndrome, peritoneal carcinomatosis, or chylothorax/chylous ascites.

Monitoring

In cases of prolonged catabolism (from approximately 5 days), artificial nutrition (enteral or parenteral) should be gradually increased over several days, and the following parameters should be monitored to prevent Refeeding Syndrome ^[1-3]:

• Phosphate <0.6 mmol/L or a drop of <30% below the normal range

Or:

• Two or more other electrolytes below the normal range:
• Phosphate <0.8 mmol/L
• Potassium <3.5 mmol/L
• Magnesium <0.75 mmol/L

Special Considerations

• Maintain or build muscle mass and physical functions, and support metabolism through regular physical activity (individually adapted endurance and resistance training).
• For advanced disease: Nutrition interventions should be determined collaboratively with the patient based on prognosis, anticipated benefits, and potential burdens.
• For terminal patients: Focus treatment on patient well-being. In cases of acute confusion, provide short and limited fluid intake to rule out dehydration as a triggering cause.

Enhanced Recovery After Surgery (ERAS)

• All surgical patients in an ERAS program should be screened for malnutrition risk and treated accordingly.
• Avoiding fasting, ensuring preoperative loading with fluids and carbohydrates, and initiating oral nutrition from the first postoperative day minimizes perioperative nutritional/metabolic reactions.
• The preoperative period should be used for "prehabilitation" with regular physical activity and nutritional therapy, particularly in functionally limited patients at risk of malnutrition.
• Alternatives to major surgery should be considered for patients with high malnutrition risk or manifest malnutrition.
• Simultaneous, sequential, or repeated surgeries, chemotherapy, and/or radiation pose a high risk of gradual deterioration in nutritional status. Adhering to the ERAS concept minimizes the nutritional and metabolic impacts of such intensive therapies ^[1-3].

Medications/Supplements

• Antiemetics for nausea/vomiting
• Antimicrobials for fungal, bacterial, or viral infections
• Analgesics for chronic pain or pain associated with chewing/swallowing or intestinal activity
• Agents to stimulate saliva production in cases of xerostomia
• Antisecretory agents to reduce excessive saliva production or vomiting in cases of impaired bowel transit
• Acid secretion inhibitors and other substances to protect against symptomatic mucosal lesions or esophageal reflux
• Agents to maintain or normalize bowel motility and to treat or prevent constipation or diarrhea
• Antidepressants, anxiolytics, mood stabilizers
• Pancreatic enzymes

Additional Recommendations, If Indicated (Low Evidence) ^[1-3]

• Corticosteroids for appetite stimulation in anorexic patients with advanced disease for a limited time span (1-3 weeks). Caution: Potential adverse effects include muscle breakdown, insulin resistance, and infections.
• Progestogens to increase appetite and weight (not lean body mass) in anorexic patients with advanced disease. Caution: Risk of serious adverse effects, such as thromboembolism.
• Long-chain N-3 fatty acids (2 g EPA/day) to stabilize or increase appetite, food intake, lean body mass, and body weight in patients with advanced disease undergoing chemotherapy who are at risk for weight loss or manifest malnutrition.
• Prokinetics for patients experiencing early satiety, after diagnosing and treating constipation. Caution: Severe potential adverse effects of Metoclopramide (on the central nervous system) and Domperidone (on heart rhythm) ^[8].
• Olanzapine may have antiemetic effects in cachectic patients, potentially enhancing appetite and positively influencing body weight ^[8].

Insufficient Consistent Clinical Data to Make a Recommendation

• Cannabinoids to improve taste disturbances or anorexia
• Androgenic steroids to increase muscle mass
• Branched-chain or other amino acids or metabolites to increase lean body mass
• Probiotics to reduce radiation-induced diarrhea
• Glutamine
• To prevent radiation-induced enteritis/diarrhea, stomatitis, esophagitis, or skin toxicity
• To improve clinical outcomes in patients undergoing high-dose chemotherapy and hematopoietic stem cell transplantation
• Low-microbial diet for more than 30 days for patients after allogeneic transplantation