It was well established that optimistic attitudes in cancer patients predict better psychological and physical adjustment to the illness both during and after the treatment (Mazanec, Daly, Douglas, & Lipson, 2010; Bozo, Gündoğdu, & Büyükaşık-Çolak, 2009). Previous studies indicated that optimism is indirectly associated with cancer patients' quality of life (QOL) through coping styles and appraisals used by the patients (Schou, Ekeberg, & Ruland, 2005). To understand whether there are other psychological mechanisms underlying the relation of optimism with quality of life and depressive symptoms of cancer patients, the current study aimed to investigate the mediator role of cancer related selfefficacy. One hundred and twenty cancer patients participated in the study and Life Orientations Test-Revised, Cancer Behavior Inventory, Beck Depression Inventory, and Multidimensional Quality of Life Scale–Cancer were administered to them. Results revealed that of the four self-efficacy domains, only the one related to maintaining activity and independence mediated the optimism-QOL and optimism-depression relations. These findings highlighted the importance of patients' beliefs in their ability to sustain their daily activities for having better physical and psychological well-being
