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BACKGROUND Cancer and dementia have often been studied in isolation. We aimed to examine the spatiotemporal trend of inpatient admissions with both cancer and dementia diagnoses. METHODS Using state-wide inpatient claims data, we identified all hospital admissions for patients aged ≥50 years with both cancer and dementia diagnoses in New York State, 2007-2017. We examined the spatiotemporal trend of the admission using a novel Bayesian hierarchical model adjusting for socioeconomic factor, as measured by Yost index. RESULTS Admissions with the presence of both cancer and dementia diagnoses represented 8.5% of all admissions with a cancer diagnosis, and the proportion increased from 7.1% in 2007 to 9.7% in 2017. The median admission rate was 3.5 (interquartile range: 2.2-5.2) hospitalizations per 1000 population aged ≥50 years, which increased from 2.9 in 2007 to 3.7 in 2017. The admission rate peaked first in 2010 followed by a smaller peak in 2014, before stabilizing at a level higher than the pre-2010 period. Taking into account the spatiotemporal heterogeneity, we found that hospitalizations among those with both cancer and dementia diagnoses were associated with a higher socioeconomic status (the posterior median relative risk for Yost index = 1.046 (95% credible interval: 1.033-1.058)). CONCLUSIONS Hospitalizations of patients with both cancer and dementia increased over time. Cancer care providers and healthcare systems should be prepared to provide prevention and management strategies and engage in complex medical decision-making for this increasingly common patient population comprised of individuals with cancer and dementia.