BACKGROUND: With prevalence estimates between 50% and 90% of people with cancer, cancer-related fatigue is one of the most common morbidities related to cancer and its treatment. Exercise is beneficial for the treatment of cancer-related fatigue. However, the efficacy of different types of exercise (i.e. cardiovascular training and resistance training) have not yet been investigated systematically and compared directly in a meta-analysis. OBJECTIVES: To compare the benefits and harms of cardiovascular training versus resistance training for treatment or prevention of cancer-related fatigue in people with cancer. SEARCH METHODS: We searched CENTRAL, MEDLINE, Embase, and five other databases in January 2023. We searched ClinicalTrials.gov and the International Clinical Trials Registry Platform for ongoing trials. We integrated results from update searches of previously published Cochrane reviews. In total, our searches included trials from inception to October 2023. SELECTION CRITERIA: We included randomised controlled trials investigating cardiovascular training compared with resistance training, with exercise as the main component. We included studies on adults with cancer (aged 18 years and older), with or without a diagnosis of cancer-related fatigue, for any type of cancer and any type of cancer treatment, with the intervention starting before, during, or after treatment. We included trials evaluating at least one of our primary outcomes (cancer-related fatigue or quality of life). We excluded combined cardiovascular and resistance interventions, yoga, and mindfulness-based interventions. Our primary outcomes were cancer-related fatigue and quality of life. Our secondary outcomes were adverse events, anxiety, and depression. DATA COLLECTION AND ANALYSIS: We used standard Cochrane methodology. For analyses, we pooled results within the same period of outcome assessment (i.e. short term (up to and including 12 weeks' follow-up), medium term (more than 12 weeks' to less than six months' follow-up), and long term (six months' follow-up or longer)). We assessed risk of bias using the Cochrane RoB 1 tool, and certainty of the evidence using GRADE. MAIN RESULTS: We included six studies with 447 participants with prostate, breast, or lung cancer who received radiotherapy or chemotherapy, had surgery, or a combination of these. All studies had a high risk of bias due to lack of blinding. Three studies had an additional high risk of bias domain; one study for attrition bias, and two studies for selection bias. Interventions in the cardiovascular training groups included training on a cycle ergometer, treadmill, an elliptical trainer, or indoor bike. Interventions in the resistance training group included a varying number of exercises using bodyweight, weights, or resistance bands. Interventions varied in frequency, intensity, and duration. None of the included studies reported including participants with a confirmed cancer-related fatigue diagnosis. The interventions in four studies started during cancer treatment and in two studies after cancer treatment. Before treatment No studies reported interventions starting before cancer treatment. During treatment The evidence was very uncertain about the effect of cardiovascular training compared with resistance training for short-term cancer-related fatigue (mean difference (MD) -0.29, 95% confidence interval (CI) -2.52 to 1.84; 4 studies, 311 participants; Functional Assessment of Chronic Illness Therapy - Fatigue (FACIT-Fatigue) scale where higher values indicate better outcome; very low-certainty evidence) and long-term cancer-related fatigue (MD 1.30, 95% CI -2.17 to 4.77; 1 study, 141 participants; FACIT-Fatigue scale; very low-certainty evidence). The evidence was very uncertain about the effect of cardiovascular training compared with resistance training for short-term quality of life (MD 1.47, 95% CI -1.47 to 4.42; 4 studies, 319 participants; Functional Assessment of Cancer Therapy - General scale where higher values indicate better outcome; very low-certainty evidence) and for long-term quality of life (MD 3.40, 95% CI -4.85 to 11.65; 1 study, 141 participants; Functional Assessment of Cancer Therapy - Anemia scale where higher values indicate better outcome; very low-certainty evidence). The evidence is very uncertain about the effect of cardiovascular training compared with resistance training on the occurrence of adverse events at any follow-up (risk ratio (RR) 2.00, 95% CI 0.19 to 21.18; 2 studies, 128 participants; very low-certainty evidence). No studies reported medium-term cancer-related fatigue or quality of life. After treatment The evidence was very uncertain about the effect of cardiovascular training compared with resistance training for short-term cancer-related fatigue (MD 1.47, 95% CI -0.09 to 3.03; 1 study, 95 participants; Multidimensional Fatigue Inventory-20 General Fatigue subscale where higher values indicate worse outcome; very low-certainty evidence). Resistance training may improve short-term quality of life compared to cardiovascular training, but the evidence is very uncertain (MD -10.96, 95% CI -17.77 to -4.15; 1 study, 95 participants; European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire-C30 Global Health subscale where higher values indicate better outcome; very low-certainty evidence). No studies reported outcomes at medium-term or long-term follow-up. AUTHORS' CONCLUSIONS: The evidence is very uncertain about the effects of cardiovascular training compared with resistance training on treatment of cancer-related fatigue in people with cancer. Larger, well-conducted studies including people with different cancer types receiving different treatments are needed to increase the certainty in the evidence and to better understand who may benefit most from cardiovascular or resistance training. Moreover, studies comparing the effects of cardiovascular and resistance training initiated before as well as after cancer treatment are needed to understand the prophylactic and rehabilitative effects of these exercise types on cancer-related fatigue.