Respiratory Versus Gastrointestinal Malignancies: Systemic Inflammation, Cardiovascular Burden, and All-Cause Mortality

Background/Objectives: Systemic inflammation is common in patients with cancer and may reflect tumor activity, disease extent, and the patient’s overall clinical condition. The systemic immune-inflammation index (SII), calculated from neutrophil, platelet, and lymphocyte counts, is a simple marker, but its relationship with tumor type, cardiovascular burden, and mortality is not fully clarified. To compare patients with respiratory system malignancies (RSM) and gastrointestinal tract malignancies (GITM) in terms of cardiovascular comorbidity, inflammatory profile, tumor-related characteristics, and recorded all-cause mortality, and to assess the association between SII and mortality. Methods: We analyzed 879 patients with solid malignancies, including 350 with RSM and 529 with GITM. SII was calculated as platelet count × neutrophil count/lymphocyte count. Cardiometabolic and cardiovascular burden was assessed according to the number of recorded cardiometabolic risk factors and cardiovascular diseases. The main outcome was recorded all-cause mortality. Results: Patients with RSM were younger and more often male, and more frequently had stage IV disease, whereas patients with GITM had a more pronounced cardiometabolic risk profile. Mortality was higher in RSM than in GITM (42.3% vs. 29.9%), and SII was also higher in RSM (median 1117.8 vs. 716.8). In the overall cohort, higher SII was associated with mortality after adjustment for age, sex, cancer type, stage, and metastatic disease (OR 1.11 per 1000-unit increase, 95% CI 1.02–1.21; p = 0.013). Mortality increased across SII tertiles from 22.5% to 34.5% and 47.4%. Adding SII to the clinical model led to only a small increase in AUC, from 0.719 to 0.729. Conclusions: SII was higher in patients with RSM and was associated with recorded all-cause mortality. However, its added prognostic value was modest. SII should therefore be interpreted as a supportive inflammatory marker, together with tumor stage, metastatic disease, and the broader clinical condition of the patient.