Study aim: Determining the effectiveness of cognitive behavioral therapy based on mindfulness on the fear of disease progression and post-traumatic growth among women with breast cancer Design: The clinical trial has an experimental and control group with parallel groups, a blind strain, on 30 women with breast cancer, randomized, and the randomization method is used. Settings and conduct: Place of study: medical oncology and hematology department of Imam Khomeini hospital in Sari city; Study population: 30 women with breast cancer; Type of blinding: single blind; How to blind: In this research, the participants are not aware of the details of the type of treatment and all attend the treatment sessions with the same environment and conditions. Therapists who are aware of the type of intervention (MBCT) implement a specific treatment method without change for everyone. Detailed information about the intervention will not be given to the participants until the end of the study to avoid bias. Participants/Inclusion and exclusion criteria: Inclusion criteria: women with breast cancer age range from 30 to 65 years old, suffering from breast cancer and willing to participate in treatment sessions. Exclusion criteria: suffering from other serious psychiatric diseases, serious physical diseases at the same time. Intervention groups: The experimental group includes women with breast cancer who participate in eight 90-minute group sessions of mindfulness-based cognitive behavioral therapy (MBCT). These sessions include mindfulness exercises, meditation and paying attention to present experiences. The control group receive no intervention and only are followed up on usual and standard care. Main outcome variables: Fear of disease progression; post-traumatic growth