BACKGROUND: Cancer-related fatigue (CRF) is one of the most common symptoms associated with cancer and its treatment. Different types of exercise have demonstrated beneficial effects on CRF. Previous evidence syntheses provided promising but inconclusive results when focusing on the effects of resistance training. OBJECTIVES: To evaluate the effects of resistance training on CRF in people with cancer and, specifically, to compare the effects of resistance training with no training on CRF at: different periods of treatment in relation to anticancer therapy (before, during, or after anticancer therapy); different periods of assessment (up to 12 weeks after the intervention, between more than 12 weeks and less than six months after the intervention, or six months or longer after the intervention). Moreover, we wanted to compare the effects of resistance training with no training on quality of life (QoL), adverse events, depression, and anxiety. SEARCH METHODS: We performed an extensive literature search in eight databases including CENTRAL, Medline, and Embase in October 2023. We searched trial registries for ongoing studies, and we integrated results from update searches of previously published Cochrane reviews. SELECTION CRITERIA: We included randomised controlled trials (RCTs) that compared resistance training with no training in adults with any type of cancer who received resistance training initiated before, during, or after anticancer therapy. Eligible RCTs needed to evaluate CRF or QoL. Resistance training had to be structured, last for at least five sessions, and include face-to-face instruction. We excluded studies that randomised fewer than 20 participants per group. DATA COLLECTION AND ANALYSIS: We used standard Cochrane methodology. For analyses, we pooled short-term, medium-term, and long-term effects (i.e. up to 12 weeks, between more than 12 weeks and less than six months, and six months or longer, after the intervention). We assessed risk of bias and certainty of the evidence using Cochrane's risk of bias tool (RoB 1), and the GRADE approach, respectively. MAIN RESULTS: We included 21 RCTs with a total of 2221 participants, with diverse types of cancer, who received resistance training initiated during (14 studies), or after (7 studies) anticancer therapy. None of the studies investigated the effects of resistance training initiated before anticancer therapy. Here, we present the results on CRF, QoL, and adverse events. Results on depression and anxiety are reported in the full review. Resistance training during anticancer therapy Resistance training probably has a beneficial effect compared with no training on short-term CRF (mean difference (MD) on Functional Assessment of Chronic Illness Therapy - Fatigue scale (FACIT-Fatigue) 3.90, 95% confidence interval (CI) 1.30 to 6.51; scale from 0 to 52, higher values mean better outcome, minimal important difference (MID) 3; 12 RCTs, 1120 participants; moderate-certainty evidence). The evidence is very uncertain about the effect of resistance training compared with no training on medium-term CRF (MD on Multidimensional Fatigue Inventory -8.33, 95% CI -18.34 to 1.68; scale from 20 to 100, higher values mean worse outcome, MID 11.5; 1 RCT, 47 participants; very low-certainty evidence). The evidence is very uncertain about the effect of resistance training compared with no training on long-term CRF (MD on FACIT-Fatigue -0.70, 95% CI -4.16 to 2.76; 1 RCT, 133 participants; very low-certainty evidence). Resistance training may have a small beneficial effect compared with no training on short-term QoL (MD on EORTC QoL Questionnaire C30 - global health (QLQ-C30) 4.93, 95% CI 2.01 to 7.85; scale from 0 to 100, higher values mean better outcome, MID 10; 12 RCTs, 1117 participants; low-certainty evidence). The evidence is very uncertain about the effect of resistance training compared with no training on medium-term QoL (MD on QLQ-C30 6.48, 95% CI -4.64 to 17.60; 1 RCT, 42 participants; very low-certainty evidence). The evidence is very uncertain about the effect of resistance training compared with no training on long-term QoL (MD on Functional Assessment of Cancer Therapy - Anemia (FACT-An) 0.50, 95% CI -8.46 to 9.46; scale from 0 to 188; higher values mean better outcome, MID 7; 1 RCT, 133 participants; very low-certainty evidence). Only two RCTs (116 participants) reported data on adverse events for both the resistance training and the control arm. The evidence is very uncertain about the effect of resistance training compared with no training on the occurrence of adverse events (very low-certainty evidence). Resistance training after anticancer therapy The evidence is very uncertain about the effect of resistance training compared with no training on short-term CRF (MD on Chalder Fatigue Scale -0.27, 95% CI -2.11 to 1.57; scale from 0 to 33, higher values mean worse outcome, MID 2.3; 3 RCTs, 174 participants; very low-certainty evidence). Resistance training may have a small beneficial effect or no effect compared with no training on short-term QoL (MD on QLQ-C30 3.87, 95% CI -1.22 to 8.97; 4 RCTs, 243 participants; low-certainty evidence). None of the studies reported data on medium-, or long-term effects on CRF or QoL. Only three RCTs (238 participants) reported data on adverse events for both the resistance training and the control arm. The evidence is very uncertain about the effect of resistance training compared with no training on the occurrence of adverse events (very low-certainty evidence). AUTHORS' CONCLUSIONS: Our review demonstrates beneficial effects of resistance training during anticancer therapy compared with no training on short-term CRF and QoL for people with cancer. Resistance training after anticancer therapy may also have a small beneficial effect on short-term QoL. Data on medium-, and long-term effects are sparse. In order to facilitate evidence syntheses beyond a narrative report of the data, investigators of resistance training programmes should report adverse events more consistently and completely for all study arms, including control groups.