Pain is said to be one of the most feared and distressing symptoms of cancer 12 and one that disrupts all aspects of life 3. Research has demonstrated that despite the effective analgesic therapy and an array of treatment modalities currently available as a result of advances in the area of neuro-oncology 4, there has not been a significant reduction in the prevalence of pain in patients with cancer 5.

Cancer pain has a significant impact on the overall quality of a cancer patient's life by influencing physical, psychological, and spiritual aspects 6. Pain is the end product of a complex process that may involve emotional, spiritual, cognitive, and sensory components 7. Cancer pain has characteristics of both chronic and acute pain. Like acute pain, cancer pain is directly associated with tissue damage. When cancer pain persists and worsens, it can serve as a sign of the progression of disease 8 and can create a sense of hopelessness because patients fear that their lives are not worth continuing or patients lose the meaning of living if they must live in pain 9.

During the past two decades, a small body of research has accumulated that suggests a relationship between pain and mood disturbance in patients with cancer. Gerbershagen et a1. 10 studied health-related quality of life inpatients with prostate cancer patients with and without pain. They found that depressive symptoms are significantly more frequent in pain patients than in patient without pain. Another study compared patients with and without pain who were matched by site and progression of disease 8. Patients with pain scored higher on measures of depression as well as anxiety, hostility, and somatization.

Pain is a multidimensional experience, far beyond a nociceptive signal. It is rooted in our socio-cultural context and belief system 11. Beliefs about cause, control, duration, outcome and blame are especially important. Even Lame et al. 12 indicated that quality of life in chronic pain is more associated with beliefs about pain, than with pain intensity.

Although certain cognitions and beliefs may be adaptive and help patients to cope with the experience of pain, others may actually contribute to increased pain and affective distress. Identification of adaptive and maladaptive pain-related beliefs and cognitions might improve our understanding of individual responses to chronic pain and contribute to more effective treatment interventions 13. Cognitive-behavioral models of chronic pain emphasize the importance of pain-related cognitions and beliefs in pain adjustment 14. Pain beliefs serve the function of helping human beings to gain a stable understanding of the events that they have, are, or will be experiencing 15. The belief that pain is understandable has been associated with better treatment compliance and use of adaptive coping strategies, while the belief that pain is mysterious has been associated with greater use of catastrophizing 16.

In chronic non-cancer pain, it is generally agreed that the meaning assigned to pain can play an important role in the experience of pain and in the response to treatment. Several studies have demonstrated the impact of pain cognition on patients' pain experience, disability, distress, non-adherence, and outcome of treatment 121718. For instance, in a study 17 after controlling for demographics, employment status and pain severity, pain beliefs and cognitions accounted for a significant amount of the variance in general activity, pain interference, and affective distress. The importance of beliefs about the meaning of symptoms, how they should be managed, ability to control pain, and worry about the future have been shown to be associated with psychological functioning, physical functioning, coping, and response to treatment 18. However, up until the last decade, very few researchers addressed the cognitive dimension of pain in cancer patients. Given the high importance of pain belief in quality of life 16, it is reasonable to assess the impact that pain beliefs, may have on depression and health-related quality of life in cancer patients. Thus, this aimed: 1) to compare depression and quality of life among Iranian cancer patients with and without pain; and 2) to determine the relationships between pain beliefs and depression and quality of life.

The results of this study provide several important implications for understanding the impact of cancer pain on patients' quality of life and depression. The findings of this study support the multidimensional notion of the cancer pain experience 8 and demonstrate the effect of cancer pain on the psychological aspect of Iranian cancer patients' quality of life. There have been few studies that directly compare emotional status of cancer patients without pain to those with pain. In contrast to the physiological components of cancer pain, there has been little prior research on other aspects of cancer pain experiences, such as psychological or emotional distress. The results of this study showed that pain has deleterious effects on cancer patients' emotional status. In this study, patients with cancer pain had significantly lower role, emotional functioning and global quality of life scores than patients without cancer pain.

Depressive symptoms are significantly more frequent in pain patients than in patient without pain. These results from the current study conducted in Iran is consistent with prior studies conducted in other countries 102526 where patients with cancer pain reported significantly higher levels of perceived emotional distress due to pain than did those without pain. Lin et al. 25 studying Taiwanese cancer patients with and without pain found that cancer patients with pain reported significantly lower levels of performance status and higher levels of total mood disturbance than did cancer patients who did not experience pain after controlling for sex, disease stage, and recruitment site. In a study of 200 American cancer patients who were experiencing pain and 169 cancer patients who were pain-free, Glover et al. 26 found that patients who experienced cancer pain scored significantly higher on anxiety, depression, anger, fatigue, confusion, and total mood disturbance. It is argued that pain might play a causal role in producing depression 27. For patients with progressive life-threatening diseases, pain can add greatly to the debilitating effects of the disease and foster hopelessness and fear 28. Cancer threatens patients' existence and cancer pain may cause suffering which leads to emotional distress for cancer patients 29.

The cognitive dimension of pain refers to the way patients think about their pain and what the pain means for them, in terms of thoughts, beliefs, attitudes, and self-efficacy expectations. The meaning patients ascribe to their pain may differ among different individuals 30. Beliefs about pain are assumed to play an important role in the process of coping by influencing both the initiation of coping strategies and a person's level of adjustment. The way a patient copes with pain is influenced by the thoughts about their pain and what the pain means for them 31. Although a considerable body of knowledge exists on the role of pain cognitions in non-cancer patients, only a few studies in cancer patients have shown that pain beliefs are associated with pain intensity. Arathuzik 32 found that cognitive and emotional factors appeared to play a central role in the response to pain and in the coping methods used to deal with pain. Also it was found that a cognitive-behavioral intervention can change the ability to decrease pain 33. Zimmerman et al. 34 found a relationship between pain intensity and psychological status. In general, the cognitive dimension of cancer pain received less attention compared to other aspects of cancer pain such as physical pain.

The results of the present study replicate and extend previous findings about relationship between pain beliefs and emotional functioning. In this study higher score on some pain beliefs and perceptions including pain permanence and pain consistency were positively and significantly associated with higher depression. Also, higher scores on pain consistency were negatively and significantly associated with global quality of life. These are similar to findings from previous studies where it was found that pain beliefs and cognitions were related to pain adjustment 172435. Asghari et al 24 studied the impact of pain-related beliefs in the adjustment to cancer pain. They asserted that higher scores on pain beliefs in cancer patients are positively and significantly associated with more severe pain and higher levels of pain interference. Also examining the effects of pain beliefs in cancer patients demonstrated that perceived control over pain had a direct effect on symptom distress and mediated the effect of beliefs about pain and pain level on symptom distress. Patients' perceived control over pain maybe an important component in pain management 35.

Although our findings should not be interpreted as indicating that negative beliefs cause mood disturbance, they do indicate the need for further research examining this relationship. It is likely that there might be a mutual relation among these variables. Greater use of longitudinal designs should help in understanding the ability of beliefs and cognitions to predict quality of life in patients who suffer from cancer related pain. However, the results of this study should be read with caution. This was a descriptive design and it would be useful to replicate this study using measures obtained by other methods, especially behavioral observations.

The findings demonstrated that Iranian cancer patients, similar to cancer patients in other countries, are affected by cancer pain in many dimensions of their lives. The similarity in these patients' responses indicates that the negative impact of cancer pain is not culture specific. It is important for clinicians to make every effort to prevent cancer pain and to relieve pain effectively and promptly. Based on experiences from Western countries, pain therapy that addresses only one component of the pain experience might be destined to fail 36. Interventions that address the multidimensional aspect of pain by relieving the patient's physical burden, psychological disturbance, and emotional distress are more likely to lead to long-term benefits, not only for patients in Western countries but also for Iranian patients. Our findings also have implications for treatment by providing an explicit rationale for targeting the reduction of maladaptive beliefs.

The authors declare that they have no competing interests.

AT was the main investigator and wrote the first draft of the manuscript. AM supervised the study, analyzed the data and wrote the final draft of the manuscript. RR supervised the study. ZT contributed to the study design. MM contributed to the data collection. All authors read and approved the final manuscript.