Background: Since 1995, UK cancer policy has been directed at organizational changes to secure improvements in treatment outcomes and quality of supportive care for cancer patients. The substantial increase in hospital-based specialist cancer nurses (SCNs) during this time suggests they have a major role to play in the delivery of supportive care. Aim: To explore how SCNs implemented their role in the context of organizational change and newly-formed multidisciplinary teams. Methods: Twenty-nine SCNs participated in observation and/or interviews, resulting in 135 hours of observation and in-depth semistructured interviews with 17 SCNs. Data were collected and analysed using a grounded theory approach. Results: The prominence of the treatment agenda the process of investigating, diagnosing and treating cancer presented the biggest challenge to the delivery of supportive care. The treatment agenda influenced how support was offered, determined professional boundaries and relegated support to a subordinate position in patient care. Conclusions: Access to supportive care is a central tenet of current cancer policy and crucial to the philosophy of patient-centred care. While SCNs are essential to the delivery of supportive care, this study highlights the challenges they encounter in organizations which prioritise treatment and improvements to treatment outcomes.