Assessing Vulnerability in Geriatric Oncology: Frailty, Multimorbidity, Functional Age, and Polypharmacy—Challenges and Opportunities

Background As more older adults develop cancer, assessing vulnerability is important because chronological age alone does not reflect their health status. However, little is known about how vulnerability is assessed in older adults with cancer. Objective This narrative review examines measurement approaches in geriatric oncology and proposes strategies for integrating frailty, multimorbidity, functional age, and polypharmacy into a clinically actionable framework. Methods We conducted a structured narrative review informed by PubMed and MEDLINE. We prioritized landmark methodological studies, major guidelines, randomized trials, widely used instruments, and representative literature relevant to conceptual development, implementation, and emerging innovations, including digital technologies and artificial intelligence. Results Current tools provide useful but incomplete assessments. Frailty and geriatric assessment–derived measures predict treatment toxicity, functional decline, and mortality, but many tools lack oncology-specific calibration, longitudinal responsiveness, and clear links to intervention. Traditional comorbidity indices are primarily prognostic and often insufficiently capture disease severity, functional impact, competing risks, or treatment-specific vulnerability. Functional age links biological and functional capacity to treatment tolerance, although standardized operationalization remains lacking. Polypharmacy contributes to vulnerability through drug interactions, regimen complexity, pharmacological burden, and functional decline, but medication-burden measures remain underused in oncology workflows. Integrating emerging oncology-specific indices, repeated assessment, digital technologies, biomarkers, and decision-support systems may improve precision and clinical applicability. Conclusions Measurement in geriatric oncology should move toward integrated, dynamic frameworks that combine frailty, multimorbidity, functional status, and pharmacological complexity while linking risk stratification to clinical action. Functional age may serve as a central organizing construct, but further validation is needed before routine use across oncology settings.