Association Between the Cancer and Aging Research Group Score and Chemotherapy Toxicity in Older Portuguese Patients: A Retrospective Single-Center Study

Background Older adults are more likely to be affected by cancer and are at higher risk of chemotherapy‑related toxicity. The Cancer and Aging Research Group (CARG) score was developed to estimate the risk of severe toxicity in older patients receiving chemotherapy, but its performance varies across settings and populations. Objective The objective of this study is to evaluate the correlation between the CARG risk score and chemotherapy‑related toxicity in older adults with solid tumors treated at a Portuguese Oncology Center. Methods We conducted a retrospective observational study of patients aged ≥65 years with solid malignancies who received chemotherapy between January and December 2023 at our center. Patients treated with immunotherapy or targeted therapies were excluded. Baseline clinical and geriatric variables were collected from electronic medical records. Toxicities were graded using CTCAE v5.0; the maximum toxicity grade per patient was recorded. Spearman's rank correlation assessed the association between the CARG score and maximum toxicity grade. Results A total of 283 patients were included (median age 73 years (range 65-93); 56.2% (n = 159) male; ECOG PS 0 in 65.4% (n = 185)). The median BMI was 25.2 kg/m²; median SCr 0.86 mg/dL; median SHb 12.4 g/dL. Overall, 84.1% (n = 238) experienced at least one chemotherapy‑related adverse event: grade 2 in 49.1% (n = 139) and grade 3-4 in 32.9% (n = 93). Fatigue (n = 88, 31.1%) and neutropenia (n = 80, 28.3%) were the most frequent toxicities. The median CARG score was 6 (range 2-18); 21.9% (n = 62) were low‑risk, 59.4% (n = 168) intermediate‑risk, and 18.7% (n = 53) high‑risk. The incidence of grade 3-4 toxicity increased across CARG categories: low 22.6% (n = 14), intermediate 41.2% (n = 69), and high 79.2% (n = 42). The CARG score correlated significantly with maximum toxicity grade (Spearman R = 0.27; p = 2.8 × 10⁻⁶). Conclusions In this real‑world Portuguese cohort of older adults with solid tumors, the CARG score was significantly associated with chemotherapy‑related toxicity, with a stepwise increase in severe events across risk categories. Although the correlation strength was modest, these findings support the use of CARG as a complementary tool to anticipate toxicity and guide shared decision‑making. Prospective studies incorporating modern systemic therapies and capturing the impact of low‑grade toxicities are warranted.