Background: Informal family caregivers play a crucial role in cancer care. Effective caregiver involvement in cancer care can improve both patient and caregiver outcomes. Despite this, interventions improving the caregiver involvement are sparse. This protocol describes a randomised controlled trial evaluating the combined effectiveness of novel online caregiver communication education modules for: (1) oncology clinicians (eTRIO) and (2) patients with cancer and caregivers (eTRIO-pc).