Malnutrition is a common and serious complication among cancer patients that negatively affects treatment response, quality of life, and overall survival. Tools such as the Patient-Generated Subjective Global Assessment (PG-SGA©) and phase angle (PA), which is derived from bioelectrical impedance analysis (BIA), have shown promise in identifying nutritional risk. Their effectiveness as mortality predictors requires further validation. Objective: Investigate the association between different nutritional assessment approaches, including the PG-SGA, body mass index (BMI), fat-free mass index (FFMI), and phase angle, and overall survival in patients undergoing systemic cancer treatment.A prospective study was conducted with 111 adult patients treated at a tertiary university hospital. Nutritional assessments were performed using the PG-SGA and BIA, and clinical and oncological data were collected. Survival analysis was performed using Kaplan-Meier curves, and mortality-associated variables were identified using Cox proportional hazards regression models.During the follow-up period, 51.4% of patients died. PG-SGA classification was strongly associated with mortality; severely malnourished patients had a 4.68-fold higher risk of death than well-nourished patients (hazard ratio [HR]: 4.68; p < 0.001), even after adjusting for tumor type. FFMI also emerged as a relevant marker, with higher mortality observed in patients with low lean body mass. Phase angle showed a significant association with survival in univariate analysis, though this association lost significance after adjusting for clinical stage.These findings suggest that a comprehensive nutritional assessment that integrates clinical and bioelectrical parameters may provide valuable information for risk stratification in oncology. The PG-SGA classification stood out as an independent predictor of mortality, and phase angle demonstrated potential as a complementary marker. The results underscore the importance of early nutritional screening as an essential component of multidisciplinary cancer care.