 Breast cancer is the most common cancer among women in the U.S. - about 1 in 8 women will develop the disease in their lifetime. Although tremendous strides have been made in its treatment, more than 40,000 deaths will be attributed to the disease in 2005 alone. These sobering and well-recognized risks are a major source of distress among women free from the disease, and among those who have completed treatment for new onset disease. Regarding the latter, clinical interventions are virtually absent during the highly stressful transitional period in coming off treatment to becoming a breast cancer survivor, and no studies have tested interventions to reduce distress, particularly fear of recurrence, and improve quality of life during this time. Therefore, we proposed to conduct a two-armed randomized wait-list controlled study on use of a mindfulness-based stress reduction MBSR intervention among 100 female breast cancer patients stages 0-III who have recently completed treatment with surgery, radiation andor chemotherapy. Specifically, we investigated: i whether MBSR favorably influences psychological status, quality of life, stress hormones, and immune status; and ii possible mechanisms by which MBSR may work, in particular, through a reduction in fear of breast cancer recurrence. Both objectives were studied at the critical transition time following completion of surgical and adjuvant therapies end of treatment to 18 months thereafter for breast cancer. The MBSR intervention included 6 weeks of class sessions according to the curriculum established by Kabat Zinn and Santorelli. Analysis of covariance models are being used to assess whether change in the above-defined outcomes varies by random assignment MBSR or wait-list, per the intention-to-treat principle. Moreover, change reduction in fear of recurrence attributed to MBSR is being investigated as a mediator. If this R21 exploratory study shows that MBSR improves patient proximal outcomes following completion of breast cancer treatment, the science will be mature enough for future large-scale evaluation of MBSR as a potential therapy to reduce long-term morbidity and mortality in breast cancer patient populations. 