The present study is the first study in comparing the effectiveness of MBCT and ACT on the FSS, improvement in PSQI and CD-RISC in a patient with prostate cancer. The primary outcomes showed that both MBCT and ACT were effective on FSS, PSQI, and CD-RISC; however, these changes did not persist until the follow-up stage. Secondary outcomes also showed that there is an inverse relationship between the FSS and PSQI and the CD-RISC. Although a similar study has not been done so far, Haller et al. (
7) checked out the effectiveness of these two treatments on the psychological indices in cancer patients. Along with the results of this study, they (
7) showed that the use of MBCT in breast cancer patients was associated with a short-term effect on fatigue, sleep and stress indices, although only changes in stress remained persistent in a six-month follow-up. In this regard, in another study Park et al. (
6) showed that eight sessions of MBCT had a significant effect on psychological status of patients with breast cancer. In addition, according to the results of a study by Lao et al. (
15) MBCT increased cognitive flexibility and supra-consciousness. Further, Britton et al. (
16) showed that the use of MBCT has been associated with improved PSQI in patients undergoing drug therapy. Along with the results of the present research, Rimes and Wingrove’s study (
8) indicated the effectiveness of MBCT on chronic fatigue syndrome. In contrast to the results of this study, based on the effectiveness of MBCT, Chambers et al. (
17) pinpointed that this treatment had no significant effect on reduction of distress in men with advanced prostate cancer.
A part of the results of this study showed that ACT was associated with a decrease in the FSS, improvement in PSQI and CD-RISC. In this regard, the results of the Daly-Eichenhardt et al. (
18) showed that acceptance and commitment therapy has significantly improved the quality of life and the psychological flexibility. In addition, Jacobsen et al. (
19) in their study indicated that ACT reduced fatigue severity in fatigue syndrome patients.
Based on the secondary outcomes of this study there is an inverse relationship between FSS, PSQI and psychosocial flexibility. In this regard, the results of Honn et al. (
20) determined that sleep disorders can reduce psychological flexibility by weakening cognitive functions, and there is a significant reverse relationship between the two variables. In contrast with results of this study, there was no significant relationship between psychosocial flexibility and fatigue in the other study by Jacobsen et al. (
19).
The results of this study showed the effectiveness of third wave interventions on the psychological indices in the metastatic cancer patient. The use of MBCT and ACT as an affordable and accessible intervention can be accompanied by clinical applications in the field of cancer. However, the results of this study, due to a single-case study, have limited generalizability. A randomized clinical trial in comparing the effectiveness of MBCT and ACT with non-treatment, placebo therapy and other effective treatments in oncology can be a good route for future studies.