This study investigates the predictive value of serum albumin levels on cancer survival, using data from the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2018. The study population was divided into two groups based on median albumin levels (≤ 4.2 g/dL and > 4.2 g/dL) and further stratified by cancer aggressiveness. Survival rates were estimated using the Kaplan-Meier method, and the Cox proportional hazards model was used to assess the association between serum albumin levels and cancer mortality. Restricted cubic spline (RCS) analysis was conducted to examine the nonlinear relationship between albumin levels and cancer mortality risk. Key findings include: - Patients with albumin levels ≤ 4.2 g/dL had lower survival rates compared to those with levels > 4.2 g/dL, regardless of cancer aggressiveness. - Adjusted for confounders, decreased albumin levels were associated with an elevated risk of cancer mortality across all groups. - RCS analyses revealed a stable nonlinear negative association between albumin levels and cancer mortality in all groups. The study concludes that low serum albumin levels predict higher cancer mortality, and a nonlinear negative association exists between serum albumin levels and the risk of cancer mortality. These findings highlight the importance of monitoring albumin levels in cancer patients to improve prognostic accuracy and guide treatment decisions.This study investigates the predictive value of serum albumin levels on cancer survival, using data from the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2018. The study population was divided into two groups based on median albumin levels (≤ 4.2 g/dL and > 4.2 g/dL) and further stratified by cancer aggressiveness. Survival rates were estimated using the Kaplan-Meier method, and the Cox proportional hazards model was used to assess the association between serum albumin levels and cancer mortality. Restricted cubic spline (RCS) analysis was conducted to examine the nonlinear relationship between albumin levels and cancer mortality risk. Key findings include: - Patients with albumin levels ≤ 4.2 g/dL had lower survival rates compared to those with levels > 4.2 g/dL, regardless of cancer aggressiveness. - Adjusted for confounders, decreased albumin levels were associated with an elevated risk of cancer mortality across all groups. - RCS analyses revealed a stable nonlinear negative association between albumin levels and cancer mortality in all groups. The study concludes that low serum albumin levels predict higher cancer mortality, and a nonlinear negative association exists between serum albumin levels and the risk of cancer mortality. These findings highlight the importance of monitoring albumin levels in cancer patients to improve prognostic accuracy and guide treatment decisions.