The present study was conducted to assess the effectiveness of acceptance and ACT on pain and quality of life in breast cancer patients. In response to the first research hypothesis that treatment based on acceptance and commitment would reduce pain in cancer patients, the results demonstrated a significant difference between the experimental and control groups in the pre-test and post-test. Based on these findings, it can be concluded that the treatment based on acceptance and commitment reduced the severity of pain in breast cancer patients. This finding is in line with the results of research conducted in this field, including the research of Wurtzen et al. (
15), Hoffman et al. (
16), Lengacher et al. (
17), Henderson et al. (
18), Kim et al. (
19), Dehghani et al. (
20), Brown and Ryan (
21), and Mousavi et al. (
22). The present study showed that the treatment based on acceptance and commitment effectively reduced pain intensity in breast cancer patients and improved their quality of life. According to research evidence, treatment based on acceptance and commitment effectively reduced pain intensity, and this treatment can reduce chronic pain. Pain is a serious problem for patients, spouses, and other family members. Research shows that the wife's reaction to the patient can be effective in her ability to cope with pain (
23).
In explaining the second hypothesis of the research, that is, the effectiveness of treatment based on acceptance and commitment to the quality of life in patients with breast cancer, the evidence showed that this treatment was effective in increasing the quality of life of patients. In this regard, the research results of Feros et al. indicated that treatment based on acceptance and commitment increased psychological flexibility and improved distress, mood, and quality of life (
6).
From the point of view of therapy based on acceptance and commitment, the primary source of problems in therapy seekers is their psychological flexibility. Limited options for behavior make a person feel trapped and conflicted. Acceptance and commitment therapy emphasizes the benefit of psychological flexibility, that is, having behavioral options available. This occurs when a person consciously accepts their troubling thoughts and feelings, behaves in the same direction, and shows consistency with their values. This happens in the treatment based on acceptance and commitment using different experimental, metaphorical, and second-degree change methods. Psychological inflexibility persists through six main interconnected processes: cognitive fusion, dependence on self-concept, experiential avoidance, lack of connection with the present, uncertain values, and weakness in respect for values. This research showed that the severity of chronic pain was reduced. The quality of life of cancer patients was increased due to psychological flexibility, which is a treatment based on acceptance and commitment using cognitive delusion, separation, and separation of self-concept, experiential acceptance, conscious contact with the present, clear and specific values, and action and commitment based on values create it. The results and achievements of the research showed the effectiveness of psychological and supportive interventions in improving the quality of life of people living with breast cancer (
4,
24). Despite the importance of the third wave of cognitive-behavioral therapies, including the approach based on acceptance and commitment, they have been announced as an important area of modern therapy, and research shows their influential role in improving the quality of life (
25). Only a few researchers have examined the application of ACT techniques in the psychotherapy of cancer patients, including the research of Hulbert-Williams et al. (
5), who found the ACT approach effective in coping with cancer. The results of other research in the field of acceptance and commitment-based treatment demonstrated that the components of this treatment promote psychological flexibility in cancer patients, which can improve the quality of life and alleviate the suffering of patients (
6).
Research findings on mindfulness as the core concept of treatment based on acceptance and commitment indicate that cancer stress management based on acceptance and awareness reduced the psychological suffering of breast cancer patients and increased their quality of life and mental health (
26).
This therapy teaches people to accept what they cannot change and what is out of their control and commit to action that makes their lives meaningful and complete. This treatment aims to help patients build a rich, complete, and meaningful life based on their values and to see the pain and suffering of life as an integral part of their lives (
8).
According to the results of the present study, this treatment method can be used as a selective and complementary psychotherapy to reduce pain intensity and increase cancer patients' quality of life. This can lead to information and enthusiasm of the relevant specialists to the psychological aspects of treatment and stimulate them to attach more importance to this aspect in breast cancer patients. The outcomes can significantly impact the treatment and recovery process. In addition, from a social and economic point of view, this can have additional positive results and benefits.