Fig. 6

Association between NPAR and all-cause mortality risk in metastatic breast cancer patients (Cox regression restricted cubic spline analysis). Based on a multivariable Cox proportional hazards regression model (Model 3) adjusting for the following variables: demographic characteristics and comorbidities (age, marital status, menstrual status, education level, hypertension, diabetes, insurance type, residential area, BMI), treatment modalities (surgery, chemotherapy, radiotherapy), and tumor characteristics (pathological type, histological type, molecular subtype), the relationship between NPAR and all-cause mortality risk in metastatic breast cancer patients was modeled using a restricted cubic spline (RCS) function. The solid red line represents the fitted hazard ratio (HR), with the light red shaded area indicating the 95% confidence interval, and the gray bars representing the distribution histogram of NPAR. The vertical dashed line (Ref = 15.9) marks the reference NPAR value, while the horizontal dashed line (HR = 1) denotes the null value. P-overall indicates the significance of the overall association, and P-nonlinear indicates the test for non-linearity.