The wasting shadow: Underweight/cachexia as a consistent predictor of adverse inpatient outcomes and escalated resource use across common solid tumors.

467 Background: Underweight/cachexia (UWC) is a debilitating syndrome common in cancer, yet its comprehensive impact on inpatient outcomes and resource utilization across different tumor types is not fully elucidated using large-scale, contemporary data. This study aimed to quantify UWC prevalence and its association with mortality, palliative care (PC) use, length of stay (LOS), and total hospital charges among inpatients with lung, breast, colon, and prostate cancer. Methods: This retrospective cohort study utilized administrative data (2018-2021) from National Inpatient Sample Database. Adults hospitalized with primary lung, breast, colon, or prostate cancer were included. UWC was identified via ICD-10 codes (R64, E40-E46, R63.4, R63.6). Multivariable logistic regression (for mortality, PC use) and gamma regression (for LOS, charges) were performed, adjusting for age, sex, race, manually computed Elixhauser comorbidity score, DNR status, payer, and income quartile. Propensity score matching (PSM) was used as a sensitivity analysis for mortality. The study protocol was developed prior to analysis. Results: Among 734,212 patients, overall UWC prevalence was 18.75%, varying by cancer type: lung (23.1%), colon (20.9%), breast (13.4%), and prostate (12.7%). In bivariate analyses, UWC was significantly associated with increased mortality (e.g., Lung OR 1.79 [1.74-1.84]), longer median LOS (e.g., Lung: 6.0 vs 4.0 days), and higher median charges (e.g., Lung: $54,696 vs $47,775; all p<0.001). Increased mortality: Lung AOR 1.20 (1.16-1.23); Breast AOR 1.43 (1.34-1.53); Colon AOR 1.26 (1.18-1.34). Increased PC utilization: Lung AOR 1.74 (1.70-1.78); Breast AOR 2.18 (2.07-2.29); Colon AOR 2.02 (1.93-2.12). Longer LOS (Adjusted Mean Ratio): Lung 1.28 (1.27-1.29); Breast 1.42 (1.39-1.44); Colon 1.52 (1.50-1.54). Higher total charges (Adjusted Mean Ratio): Lung 1.15 (1.14-1.17); Breast 1.23 (1.20-1.25); Colon 1.34 (1.31-1.36) (all p<0.001). PSM for mortality yielded consistent, significant associations: Lung AOR 1.15 (1.11-1.18); Breast AOR 1.21 (1.13-1.29); Colon AOR 1.24 (1.17-1.32); Prostate AOR 1.33 (1.23-1.43). Conclusions: UWC is a significant and prevalent comorbidity among hospitalized patients with common solid tumors, consistently predicting increased inpatient mortality, palliative care utilization, prolonged LOS, and greater hospital charges, even after extensive adjustment. These findings underscore UWC as a critical marker of patient vulnerability and a driver of healthcare resource intensity. Proactive identification and integrated management strategies for UWC, including nutritional support and early palliative care, are crucial quality improvement targets to potentially enhance patient outcomes and optimize resource allocation in oncologic care.