ABSTRACTBackgroundIt is known that cancer can cause loss of body weight and muscle protein wasting, which leads to a state of malnutrition, which in turn worsens the prognosis and health of the cancer patient. It has been suggested that the promoting mechanism of this state is systemic inflammation, for which reason several clinical trials have used omega-3 fatty acids, especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), as adjuvants to antineoplastic treatment, mainly due to its anti-inflammatory effects. However, few systematic reviews and meta-analyzes have analyzed the effects of omega-3s in patients with breast cancer.ObjectiveThe aim of this study is to assess the effect of the supplementation with omega-3 fatty acids on nutritional and clinical outcomes in patients with breast cancer receiving medical treatment.MethodsA systematic review will be conducted, starting with a search in PubMed, CENTRAL and EMBASE using search terms related to omega-3 fatty acids and breast cancer. We will include only randomized controlled trials that assess the effects of omega-3 in patients with breast cancer receiving medical treatment.. Data will be extracted in a spread sheet. Study selection and data extraction will be conducted by two reviewers independently and the Cochrane Risk of Bias Tool for RCT will be used for assessment of risk of bias. Discrepancies will be reviewed with a third reviewer.ConclusionThis systematic review aims to provide an analysis on the outcomes of the usage of the intervention with omega-3 fatty acids on nutritional and clinical aspects in patients with breast cancer receiving medical treatment.