Objectives: Mindfulness-based intervention has been receiving growing attention in cancer care. This study aimed to examine feasibility and to preliminary explore effectiveness of mindfulnessbased cognitive therapy (MBCT) in Japanese breast cancer patients, and to explore possible modification of the program so that it fits better with this population. Methods: Twelve participants with diagnosis of Stage I-III breast cancer received an eight session, weekly MBCT intervention in a group therapy format. The participants were followed up until 3 months after the completion of the program. Results: All the participants completed the program with high attendance rate (mean number of attended sessions = 7.7). Significant improvement in anxiety (Hospital Anxiety and Depression Scale (HADS) - anxiety subscale
effect size Cohen's d = 0.88, P &lt
0.05), trauma-related psychological symptoms (Impact of Event Scale-revised
d = 0.64, P &lt
0.01) and quality of life (Functional Assessment of Cancer Therapy-Breast Cancer: FACT-B
d = 0.72, P &lt
0.01), and trend-level improvement in depression (HADS - depression subscale
d = 0.53, P = 0.054) were observed. Qualitative analyses suggested the program may be beneficial for alleviating fear of cancer recurrence and for increasing spiritual well-being. Some recommended modification of the program was indicated from the post-intervention interviews. Conclusions: Mindfulness-based cognitive therapy was well accepted by Japanese breast cancer patients and yielded favorable effect on their psychological status and quality of life. Further effectiveness study in a randomized-control design is warranted.