The Mindfulness-Based Cancer Recovery (MBCR) program at the Tom Baker Cancer Centre in Calgary, Canada began in 1996, and has been offered continuously to patients and support people since. Based on intensive training in mindfulness meditation and gentle Hatha yoga, the MBCR program has been adapted from Mindfulness-Based Stress Reduction (MBSR) to meet the needs of a cancer population. We recently completed a 5-year multi-site randomized controlled trial comparing the effects of MBCR to Supportive-Expressive Group Therapy (SET) and a one-day stress management seminar (SMS) on psychological and biological outcomes in breast cancer survivors (the MINDSET trial). In addition to comparing aggregate group outcomes over a 12-month follow-up period, we assessed baseline program preference and a number of background variables as moderators of treatment outcome, including personality characteristics, emotional suppression and repression. 272 women who had completed breast cancer treatment enrolled in the trial. Overall, greater improvements were seen on the MBCR group on measures of stress, mood disturbance and quality of life compared to the other groups post-program. Preference data was available for 161 women. The most preferred program was MBCR (55%), and overall less neurotic women preferred the SMS, while more extraverted women preferred MBCR. Only 31% of participants were assigned to their preferred treatment group, but those who got their preference improved more over time on global quality of life and stress symptoms, compared to those assigned to a non-preferred intervention. Of the moderator variables, the only significant predictor of better treatment outcomes was neuroticism, wherein those with higher baseline neuroticism, compared to those with lower levels, showed greater reduction in mood disturbances after SET, but not the other programs. These results suggest that using baseline preferences and personality characteristics to help choose appropriate interventions may have substantial merit in optimizing patient outcomes in psychosocial oncology.