Background: Cancer-associated cachexia is a multifactorial wasting disorder characterized by anorexia, unintentional weight loss (WL, skeletal muscle mass with or without loss of fat mass), progressive functional impairment, and poor prognosis. This systematic literature review (SLR) examined the relationship between cachexia and survival in patients with colorectal or pancreatic cancer. Methods: The SLR was conducted following PRISMA guidelines. Embase and PubMed were searched to identify articles published in English between 1 Jan 2016 and 10 Oct 2021 reporting survival in adults with cancer and cachexia or at risk of cachexia, defined by International Consensus (IC) diagnostic criteria (Fearon et al., Lancet Oncol 2011;12:489–95) or a broader definition of any WL. Included publications were of studies in ≥100 patients with colorectal or pancreatic cancer. Results: Twenty-six publications in patients with colorectal (n=13) or pancreatic cancer (n=13) met eligibility criteria. Included studies were observational and primarily from Europe and the United States. Eleven studies (42%) reported cachexia using IC criteria and 15 studies (58%) reported any WL. An association between survival and cachexia/WL was assessed across studies using multivariate (n=23) or univariate (n=3) analyses and within each study across multiple WL categories. Cachexia/WL was associated with a statistically significantly poorer survival in at least one WL category in 16 of 23 studies that used multivariate analyses and in 1 of 3 studies (33%) that used univariate analyses. Of the 17 studies demonstrating a significant association, 9 were in patients with colorectal cancer and 8 were in patients with pancreatic cancer. Conclusions: Cachexia/WL was associated with significantly poorer survival in patients with colorectal or pancreatic cancer in nearly two-thirds of the studies. The classification of WL varied across and within studies (multiple categories were evaluated) and may have contributed to variability. Nonetheless, awareness of cachexia and routine assessment of weight change in clinical practice in patients with colorectal or pancreatic cancer could inform early disease management strategies that may improve prognosis.