Older adults with cancer are at high risk for malnutrition and cachexia, particularly when undergoing chemotherapy. Despite this, nutritional risk is often under-recognised and under-treated in this population. This systematic review highlights that malnutrition is common both before and during chemotherapy, with digestive symptoms and weight loss frequently observed. Malnutrition is associated with poorer tolerance to chemotherapy, early treatment discontinuation, increased toxicity, and higher mortality. The authors recommend routine nutritional assessment and early, individualised interventions as part of comprehensive geriatric oncology care.