Serious mental illness (SMI) is associated with poorer cancer outcomes. Reasons for such inequalities are unclear; those with this comorbidity receive fewer specialist interventions and die earlier than the general population. Further exploratory work is required.

Exploring the experience of SMI and cancer from the perspective of those affected by this comorbidity and those caring for them professionally or informally.

Semi-structured interviews were conducted with ‘key patients’ living with SMI who had received a cancer diagnosis (n = 7), significant others who had supported key patients (n = 4) and healthcare professionals who had worked with at least one KP (n = 17). A panel of patients and professionals ratified interview guides. Interviews were analysed thematically.

Mental health professionals were more confident in their knowledge of the needs of this population than oncology professionals, but were challenged by working with patients with major physical health needs. Key patients’ mental health appeared to remain stable after cancer diagnosis, and they expressed altruism towards others with comorbid cancer and SMI. Significant others and healthcare professionals were more likely to critique systemic aspects of care than were key patients.

Professionals feel challenged when working outside of their usual job role. Training needs include mental illness awareness in an oncology setting. Improved coordination and communication is required, encompassing significant others as well as professional groups. SMI may protect against the psychological impact of cancer. Key patients were keen to provide advice and support to others in similar situations. Further research is needed into these areas.

The authors have not supplied their declaration of competing interest.