Methods: An AB form of single-subject experimental design was used in this study with 3 baselines (every 10 days) before intervention stage and two measurements during intervention stage and one follow-up (after two month). Our statistical population was chosen from women who had referred to radiotherapy department of Imam Hussein Hospital in Tehran. Out of them, 3 patients whose age range was 20 to 55 years, with non-metastatic tumor, no prior history of psychiatric disorders before cancer, scored >20 (moderate depression) by Beck Depression Inventory, were selected through purposeful sampling. Intervention included 8 sessions of 60 minutes of metacognitive therapy once a week, which has been designed to suit of the patients with specific needs. Beck Depression Inventory (BDI), Ruminative Response Scale (RRS), and Depression Metacognitive Beliefs Scale (DMB-S) were employed to collect the data. 

Results: The result of the analysis showed that the highest level of improvement in depression was 56% and the lowest level was 37%. In addition, the highest percentage of improvement in ‘thought rumination’ was 35%, while the lowest percentage of improvement was 21%. Finally, the highest percentage of improvement in ‘depression metacognitive beliefs’ was 87%, whereas the lowest percentage was 58%. In summary, the results indicated that metacognitive therapy would result in decrease of depression scores (in BDI scale), ‘thought rumination’ and ‘depression metacognitive beliefs’ (in DMB scale) and this effectiveness was persistent after two months follow-up. 

Conclusion: It seems that metacognitive therapy can help women with breast cancer to reduce their depression and ‘thought rumination.’