Shifting drivers of hospitalization in endometrial cancer: Toxicity-like organ failure phenotypes in the modern treatment era.

11066 Background: Frontline endometrial cancer care has rapidly shifted toward immune-based regimens. Whether inpatient admissions have concurrently shifted toward toxicity-like organ failure syndromes, with changing ICU use and rescue outcomes, remains unknown. Methods: We performed a survey-weighted analysis of the National Inpatient Sample (NIS) 2016–2023. Adult hospitalizations with endometrial cancer in any diagnosis position (C54/C55) were included; admissions with palliative care coding (Z51.5) were excluded. Eras were defined as 2016–2017 versus 2018–2023. Toxicity-like organ failure phenotypes were identified using ICD-10-CM proxies including pneumonitis or respiratory toxicity, colitis or diarrhea, myocarditis or pericarditis, hepatitis or liver failure, neutropenic sepsis, acute kidney injury, and electrolyte collapse. A broader sensitivity phenotype additionally included endocrine crises. ICU escalation was proxied by mechanical ventilation or shock. Major complications were defined using a composite bundle, and failure-to-rescue was defined as death among complication admissions. Outcomes included in-hospital mortality, ICU escalation, complications, length of stay (LOS), cost, and routine discharge. Results: Among 74,895 unweighted endometrial cancer hospitalizations, 25.8% occurred in 2016–2017 and 74.2% in 2018–2023. Overall inpatient mortality was 1.86% (95% CI 1.66%–2.07%) in 2016–2017 and 2.09% (95% CI 1.96%–2.22%) in 2018–2023. Hospitalizations involving any toxicity-like organ failure phenotype increased from 34.3% (95% CI 33.4%–35.1%) in 2016–2017 to 45.2% (95% CI 44.7%–45.7%) in 2018–2023. Pneumonitis or respiratory toxicity increased from 6.23% to 9.91%, acute kidney injury from 14.9% to 21.0%, and electrolyte collapse from 23.7% to 31.7%. ICU proxy use increased from 2.50% (95% CI 2.27%–2.73%) to 3.30% (95% CI 3.15%–3.45%), driven by higher shock coding (0.82% to 1.61%). Major complications increased from 36.1% (95% CI 35.3%–36.9%) to 46.5% (95% CI 46.0%–47.1%). Mortality among admissions with toxicity-like organ failure decreased modestly from 4.75% (95% CI 4.25%–5.30%) to 4.25% (95% CI 4.00%–4.52%), while mortality among ICU-level admissions remained high and unchanged (29.7% vs 29.2%). Routine discharge declined from 66.6% (95% CI 65.6%–67.6%) to 62.2% (95% CI 61.7%–62.7%), and LOS increased in the modern era (mean 5.22 days, 95% CI 5.16–5.28). Conclusions: From 2016–2023, endometrial cancer hospitalizations increasingly involved toxicity-like organ failure phenotypes with rising ICU escalation and complication burden, while inpatient mortality changed minimally. These findings highlight a growing disconnect between outpatient therapeutic advances and inpatient recognition and rescue capacity.