A growing number of people live with cancer and dementia. Dementia creates a particular set of challenges in all aspects of cancer treatment and care, including diagnosis, decision-making, access to appointments, monitoring of signs and symptoms of cancer and side effects of cancer treatment, and management of self-care tasks. People with cancer and dementia often require extensive support from family carers, and those without family support face additional challenges. This article uses the emerging UK evidence base on cancer and dementia to discuss the challenges that arise when providing cancer treatment and care to people with dementia and their families, and to make research-based recommendations on how to improve service provision for that population.