In healthcare, health risk assessments are influenced by technical ‘objective’ measurements of the physical body and disease; the values that underlie professional practices (such as beneficence, non-maleficence, and autonomy); the organisations healthcare professionals work for; and subjective belief systems of individual healthcare professionals. As a result, cancer treatments prescribed for older adults can be tempered by personal views about a patient’s age, and other age-associated health conditions or comorbidities that they may have. Drawing from interviews undertaken with nine key staff members in a large cancer service, we examine how treatment recommendations and decisions are determined when older adults with cancer also have dementia; two health conditions more common in older age. Our analysis reveals two themes that underlie the complicated processes of risk-benefit assessment in treatment decision-making: the unequal distribution of capital and power between health workers; and whether older adults with cancer and dementia are assessed as solely individuals or embedded in supportive social networks (individual versus relational autonomy). This analysis exposes capital and personal beliefs about dementia are implicit in health risk assessments for older adults who have cancer and dementia which, in conjunction with organisational constraints, significantly influence how treatment recommendations and decisions are reached.