OBJECTIVE: Assess the feasibility of conducting a cluster randomized controlled trial (RCT) comparing technology-delivered mindfulness-based intervention (MBI) programs against a waitlist control arm targeting advanced cancer patients and their informal caregivers. METHODS: Two-arm cluster RCT within Kaiser Permanente Northern California. We recruited patients with metastatic solid malignancies or hematological cancers and their informal caregivers. Intervention-group participants chose to use either a commercially available mindfulness app (10-20 min/day) or a webinar-based mindfulness course for 6 weeks. The waitlist control group received usual care. We assessed feasibility measures and obtained participant-reported data on quality of life (QoL; primary outcome) and distress outcomes (secondary) pre- and postintervention. RESULTS: A hundred and three patients (median age 67 years; 70% female; 81% White) and 39 caregivers (median age 66 years; 79% female; 69% White) were enrolled. Nearly all participants chose the mindfulness app over the webinar-based program. Among the participants in the intervention arm who chose the mobile-app program and completed the postintervention (6-week) survey, 21 (68%) patients and 7 (47%) caregivers practiced mindfulness at least 50% of the days during the 6-week study period. Seventy-four percent of intervention participants were "very" or "extremely" satisfied with the mindfulness program. We observed improvements in anxiety, QoL, and mindfulness among patients in the intervention arm compared to those in the control group. CONCLUSIONS: We demonstrated the feasibility of conducting a cluster RCT of mHealth MBI for advanced cancer patients and their caregivers. Such remote interventions can be helpful particularly during the COVID-19 pandemic.