Fatigue is the most common symptom experienced by patients during the cancer trajectory from diagnosis to the end of life and is defined as a distressing, persistent, subjective sense of physical, emotional and/or cognitive tiredness or exhaustion related to cancer or cancer treatment that is not proportional to recent physical activity and that interferes with usual functioning. 1, 2 Cancer-related fatigue (CRF) is different from other types of fatigue by its severity and persistence and the inability to alleviate it through rest or sleep. CRF affects almost 65% of patients with cancer; over two-thirds of these patients describe CRF as severe for at least 6 months and one-third reports this as persistent fatigue for a number of years after treatment. 3, 4, 5 Up to 40% of patients report fatigue at cancer diagnosis, 80%–90% during chemotherapy (ChT) and/or radiotherapy (RT), in particular 17%–21% during ChT alone and 33%–53% during association of ChT and RT. 2, 3 Moreover, hormonal therapy, targeted therapy and also immunotherapy can be responsible for fatigue. CRF related to immunotherapy has an incidence from 12% to 37% up to 71% when immunotherapy is combined with ChT, monoclonal antibodies, antiangiogenic agents and targeted therapies. In addition, immunotherapy can be a cause of fatigue when it is complicated by endocrinological disorders. 6, 7

The aetiology of CRF has not yet been thoroughly elucidated, although it may involve several physiological and biochemical systems which, in turn, might vary according to the type of tumour, stage of disease and treatment. 1, 3, 8