APS-TMA phenotypes as a failure-to-rescue signal during U.S. cancer hospitalizations: National Inpatient Sample, 2018–2022.

11041 Background: Failure-to-rescue (FTR), defined as mortality following major inpatient complications, reflects both patient disease pathology and hospital rescue capacity. Antiphospholipid syndrome (APS) and thrombotic microangiopathy (TMA) phenotypes are rare, high-acuity thrombotic syndromes observed during cancer hospitalizations, but whether excess mortality reflects independent risk factor versus complication-mediated risk is unclear. Methods: A serial cross-sectional, hospitalization-level analysis was performed using the 2018–2022 Healthcare Cost and Utilization Project National Inpatient Sample (NIS). Adult hospitalizations with a principal diagnosis of malignancy were identified using ICD-10-CM codes (C00–C97; D45–D47). APS and TMA phenotypes were defined using any-diagnosis ICD-10-CM proxies for APS and TMA, including TTP/HUS, and combined as an APS/TMA phenotype. Because laboratory and medication data are unavailable in the NIS, exposures were analyzed as inpatient phenotypes rather than presumed diagnoses. Major complications included mechanical ventilation and acute kidney injury requiring dialysis. Failure-to-rescue was defined as in-hospital mortality among admissions with ≥1 major complication. National estimates incorporated discharge weights, hospital clustering, and stratification; multivariable models adjusted for All Patient Refined Diagnosis Related Group (APR-DRG) severity. Results: Among an estimated 4.81 million principal malignancy hospitalizations nationally, APS/TMA phenotypes occurred in 0.48% of admissions. Compared with non-phenotype admissions, APS/TMA phenotype hospitalizations had higher mortality (9.43% vs 4.35%) and higher rates of major complications, including mechanical ventilation (5.85% vs 2.57%) and dialysis-requiring acute kidney injury (2.11% vs 0.61%). In severity-adjusted modeling incorporating APR-DRG severity, APS/TMA phenotype was not independently associated with mortality (adjusted OR 0.99, 95% CI 0.70–1.40), indicating that excess mortality was largely mediated by complications and underlying illness severity. Conclusions: APS/TMA phenotypes identify a rare but high-acuity subgroup of cancer hospitalizations characterized by disproportionate ICU-level support and dialysis utilization, functioning as a national failure-to-rescue signal rather than an independent driver of mortality after severity adjustment. These findings highlight the importance of early recognition and severity-directed rescue strategies for high-risk thrombotic phenotypes during cancer admissions.