This prospective observational study aims to evaluate and compare the effectiveness of three geriatric assessment tools-CARG (Cancer and Aging Research Group score), G8 screening tool, and Frailty Scale-in predicting chemotherapy-related toxicity (CRT) in cancer patients aged 65 years and older. A total of at least 100 patients receiving standard chemotherapy (excluding hematologic malignancies and immunotherapy) at Çanakkale University Medical Faculty Oncology Clinic will be assessed prior to treatment initiation. Each participant will undergo baseline evaluations including G8, CARG, and Frailty assessments. The study will analyze the correlation between these tools and the occurrence of CRT using AUC, logistic regression, and correlation analyses. The goal is to identify the most accurate and practical screening tool to guide clinical decision-making and minimize chemotherapy toxicity in older adults.

Inclusion Criteria:

• Patients aged 65 years or older.
• Histologically confirmed cancer diagnosis with a pre-planned chemotherapy regimen (adjuvant, neoadjuvant, or palliative intent).
• Chemotherapy not yet initiated at the time of enrollment.
• Clinically stable condition, as assessed by the oncologist.
• Willingness and ability to provide written informed consent.

Exclusion Criteria:

• Presence of acute infection or advanced organ failure (cardiac, hepatic, or renal).
• Severe psychiatric illness or cognitive impairment that interferes with the ability to complete assessments.
• Patients receiving concurrent hormonal therapy, targeted therapy, immunotherapy, or radiotherapy.
• Diagnosis of hematologic malignancies (e.g., leukemia, lymphoma, myeloma).

The study population will consist of adult oncology patients aged 65 years and older who are scheduled to receive systemic chemotherapy for solid tumors at the Çanakkale Onsekiz Mart University Medical Faculty, Department of Medical Oncology. Eligible participants must have a confirmed cancer diagnosis and a predefined chemotherapy regimen (adjuvant, neoadjuvant, or palliative), but must not have yet started treatment at the time of enrollment.