Malnutrition and sarcopenia are highly prevalent but often under-recognised and under-treated in adults with cancer. Both conditions are associated with poorer treatment tolerance, reduced quality of life, and worse clinical outcomes. This COSA position statement provides practical recommendations for routine screening of all cancer patients for malnutrition and sarcopenia, using validated tools. It emphasises early identification, comprehensive assessment, and timely, individualised interventions—including nutrition therapy, exercise, and multidisciplinary care. The statement highlights the importance of integrating nutrition and muscle health into standard oncology practice to improve patient outcomes and recovery.