Purpose: Delirium is a prevalent neuropsychiatric syndrome in older people with cancer. However, there are no meta-analyses assessing its incidence exclusively in this population. This study aims to assess the incidence proportion of delirium in older people with cancer in the hospital area.

Methods: A systematic review and meta-analysis were carried out. MEDLINE, Scopus, and EBSCO were searched from inception to December 2021. PRISMA guidelines were followed. Inclusion criteria were original peer-reviewed studies with experimental (randomised controlled trials), observational, and cross-sectional designs assessing delirium older inpatients (≥65 years) with oncological diseases in medical and post-surgical hospital areas and using validated screening or diagnostic methods. A web-based system was used to manage the screening process. Study quality was assessed with Joanna Briggs Institute Critical Appraisal tools. The statistical analysis was performed in RevMan v5.4.0 (Cochrane Collaboration, Oxford, UK), using a random-effects model to calculate incidence and 95% confidence intervals (CIs).

Results: Based on 37 included articles, the incidence proportion of delirium ranged from 3.8% to 61.4%, in a total of 11,847 older patients with cancer. Meta-analysis showed a pooled incidence of 22.6% (95% confidence interval 18.5%, 26.7%; I(2) = 97%, p < 0.001). The main tools for detection were the Diagnostic Statistical Manual criteria and the Confusion Assessment Methods scale.

Conclusions: The incidence proportion of delirium in older inpatients with cancer is 22.6%. Incidence in the medical setting was higher than in the post-surgical areas. There is a need for high-quality studies examining delirium in older people with cancer.