A Narrative Review on Karnofsky Performance Status in Patients With Brain Tumors: Should It Be Adjusted?

The Karnofsky Performance Status (KPS) is one of the most widely used functional scales in oncology to assess patients' functional status, including their ability to work, perform self-care, and the need for assistance.Although its clinical utility is well established, KPS is generally applied uniformly across cancer populations, without specifically accounting for the distinct patterns of disability observed in patients with brain tumors.These patients may experience focal neurological deficits, cognitive impairment, and other neurological changes that can substantially affect functional status and may not be adequately captured by the current KPS framework.This narrative review examines the available evidence regarding the limitations of the standard KPS in patients with primary and metastatic brain tumors and considers the potential value of adjusting or complementing its use in clinical practice and research.A non-systematic literature review was conducted between August and September 2026 in PubMed and Google Scholar, using terms including "Karnofsky Performance Status," "KPS," "brain metastasis," "brain tumor," "neuro-oncology," "glioma," and "radiotherapy" in various combinations.Studies published in English were considered, with priority given, when possible, to studies published within the past five years and to those comparing KPS with neurological, cognitive, or patient-reported measures of function.The reviewed literature demonstrates substantial interobserver variability in KPS assignment, with kappa coefficients as low as 0.19-0.26 in studies reporting poor agreement.Discordance was also identified between clinician-assigned KPS and objective cognitive impairment, with up to 36% of patients considered to have good KPS scores showing clinically relevant cognitive dysfunction.In addition, medical decision-making capacity may be impaired despite high KPS scores, with only 46% of patients with KPS 90-100 classified as capable using a standardized instrument.Discordance between KPS and patient-reported outcomes was also reported.These limitations have prompted the development and use of complementary tools, including the Neurologic Assessment in Neuro-Oncology (NANO) scale and brain tumor-specific assessments of instrumental activities of daily living (IADL).Overall, the KPS retains important prognostic and practical value; however, the available evidence supports complementing its use in neuro-oncology with objective neurological assessment, brief cognitive screening, and, when possible, patient-or caregiver-reported measures.Functional status should also be assessed dynamically over time, avoiding anchoring the patient's overall functional assessment to a single KPS value, rather than using KPS as the sole and sufficient measure of functional status.