Background: Cancer cachexia, often referred to as cancer wasting, is a multifactorial syndrome characterized by involuntary weight loss, muscle wasting, and systemic inflammation. It affects up to 80% of patients with advanced malignancy and is a major cause of morbidity and mortality. Despite increasing recognition, it remains underdiagnosed and inadequately treated. Objective: This meta-analysis aimed to evaluate the prevalence, clinical consequences, and effectiveness of interventions for cancer cachexia across malignancies. Methods: A systematic search was conducted in PubMed, Scopus, Web of Science, and Cochrane Library up to December 2024. Randomized controlled trials (RCTs), cohort studies, and meta-analyses reporting prevalence, outcomes, or interventions in adult cancer patients were included. Studies were pooled using a random-effects model. Primary outcomes were prevalence and overall survival; secondary outcomes included treatment tolerance, quality of life, and intervention efficacy. Results: Forty-eight studies comprising 23,400 patients were analyzed. The pooled prevalence of cachexia was 49.2% (95% CI 43.1–54.8), highest in pancreatic (74%) and lung cancer (63%) populations. Cachexia was associated with a 41% higher risk of mortality (HR 1.41; 95% CI 1.23–1.61) and reduced chemotherapy tolerance (RR 1.38). Nutritional interventions alone were insufficient, whereas multimodal approaches (nutrition, pharmacologic agents, exercise) improved weight stabilization and quality of life. Anamorelin drug showed moderate efficacy in increasing lean body mass, though survival benefit remained unproven. Conclusion: Cancer cachexia is highly prevalent and clinically significant, yet interventions remain suboptimal. Early identification and multimodal treatment should be integrated into oncology practice. Future research must focus on biomarkers, standardization of diagnostic criteria, and novel therapeutic targets.