Development of a composite risk score for chemotherapy toxicity and unplanned hospitalization in older adults with cancer: A prospective cohort study.

1659 Background: Older adults receiving chemotherapy are at high risk for severe treatment-related toxicities, which may compromise treatment completion and lead to unplanned hospitalizations. We developed a composite risk score integrating the components of Cancer and Aging Research Group (CARG) chemotherapy toxicity score and proved clinical predictors to enhance prediction of grade 3–5 (G3–5) chemotherapy-related toxicities, treatment tolerance, and unplanned hospitalization. Methods: Patients aged ≥70 years with solid tumors initiating chemotherapy were enrolled between December 2024 and August 2025 at a tertiary hospital in Shanghai, China. The primary endpoint was the occurrence of any G3–5 chemotherapy-related toxicity; secondary endpoints included chemotherapy incompletion and unplanned hospitalization. Baseline characteristics included the CARG score, tumor- and treatment-related characteristics, and laboratory parameters. Toxicities (graded using CTCAE v5.0 ), treatment completion, and unplanned hospitalizations were assessed at each cycle for up to 6 months or until completion of the planned treatment course. Predictors of G3–5 toxicities were screened by LASSO-penalized multivariable logistic regression, and model discrimination was evaluated by receiver operating characteristic curve. Results: Among 242 patients (median age 74 years; range 70–88), 71.9% were male, 64.5% had gastrointestinal malignancies, and 73.1% had stage IV disease. Overall, 164 patients (67.8%) experienced G3–5 toxicities, and 63 (26.0%) had unplanned hospitalizations. The score system included cancer type, hemoglobin, estimated glomerular filtration rate, falls within 6 months, medication management ability, C-reactive protein/albumin, MAX2 index, walking ability, and social activity level. The median score was 10 (range 6–14). Each one-point increase in score was associated with higher risk of any G3–5 toxicity (OR 1.21, 95% CI 1.14–1.30; AUC 0.75) and non-hematologic G3–5 toxicity (OR 1.19, 95% CI 1.12–1.27; AUC 0.73).The score was also positively associated with unplanned hospitalization (OR 1.07, 95% CI 1.01–1.13; AUC 0.62), but was inversely associated with chemotherapy incompletion (OR 0.93, p=0.019), suggesting more proactive treatment modifications in high-risk patients. In this cohort, the new score showed superior discrimination for any G3–5 toxicity, with a higher AUC than the CARG score (0.75 vs. 0.63). The optimal cutoff point of any G3–5 toxicity was 7.5 with relatively good specificity (72%) and sensitivity (65%). Conclusions: The composite score may help predict G3–5 toxicity, non-hematologic G3-5 toxicities, and unplanned hospitalization, potentially outperforming the CARG score. External validation and evaluation of clinical utility are warranted.