Selection of articles

Two researchers independently searched the databases and, following the proposed criteria, selected the articles. Initially, the selection was based on reading the titles and abstracts, using a standardized spreadsheet method. In a second step, the full text was read, with the subsequent methodological quality assessment. At the end of each stage, the reviewers met and submitted their results for comparison. The discrepancies were discussed, and, in cases where they were not resolved, a third reviewer was consulted to clarify doubts.

Evaluation of the methodological quality

For the assessment of the methodological quality, two reviewers independently used the instrument developed by Loney for cross-sectional studies; the quality criteria defined by authors¹³ for case report; the Newcastle-Ottawa Scale (NOS) for cohort studies; the check-list proposed by Downs and Black for randomized and non-randomized clinical trials^14,15.

The evaluation of cross-sectional studies consisted of the items sample, source of the sample, sample size, measurement of the outcome, impartial interviewer, response rate, the prevalence with CI95%, and similar participants, in which each appropriate item received a point¹³. Studies with seven to eight points were considered of high methodological quality, those with four to six points were of moderate quality, and studies with zero to three points were of low quality. The NOS, consisting of eight items and three dimensions - selection, comparability, and outcome, was developed by Wells to evaluate cohort and case-control studies. The total score can vary from zero to nine stars, where a star corresponds to one point, and two stars can be assigned to the comparability dimension. Studies between six and nine points were considered of high methodological quality, four and five points with moderate quality, and less than four points with low quality^16-18.

The checklist for randomized and non-randomized clinical trials consists of 27 items with the domains reporting, external validity, bias, selection and power bias, with each item scoring zero or one, except for item five that can score zero, one or two. The studies with a score equal to or greater than 20, were considered of high quality, 15 to 19 of moderate quality and less than or equal to 14 points low quality^14,15.

The evaluation of the case reports was based on the eight proposed items¹⁹. The items involve diagnosis, consent, approval by the ethics committee, details of the intervention, relevant clinical outcomes, patient perception, associated risks, eligibility criteria. Each item received one point when met, which are stratified at cut points equal to those of cross-sectional studies in high, medium, and low methodological quality. The scores obtained in the instruments were not used as an exclusion criterion for the articles but as indicators of the methodological quality of the studies.

Characteristics of the studies

Figure 1 summarizes the search process and the identification of relevant studies. The electronic search strategy retrieved 588 studies; of these, 512 were excluded after reading the title and abstract for not meeting the eligibility criteria, and eight for being duplicated. Thus, the full analysis of 68 studies was carried out, and of that process, 13 studies^20-32 met the eligibility criteria and were included in the review.

Figure 1 Flowchart of the steps of the systematic review recommended by PRISMA 

The 13 articles included were published from 2007 to 2018, mostly between 2012 and 2018. There was a higher concentration of studies in the United States^20,23-26. The sample size varied between 1 and 883 participants. The average ages were from 43 to 65 years; in nine studies^{(20,23-25,27-30,32 )}where the participants were men and women, and in the others only women. Regarding the design, nine studies are cross-sectional^23-26,28-32; two are clinical trials^22,27; one is a case study²¹ and two are cohort studies^20,28. As for the place of selection of the participants, most were selected in a hospital^{22,25,27-30,32}. Table 1 shows the characteristics of these studies.

Among the studies evaluated by the instrument proposed by Loney, four^26,28,29,32 achieved moderate methodological quality; five^23-25,30,31 obtained low quality. As for the studies analyzed by the NOS, both^25,28 presented moderate quality. The clinical trials^22,27 evaluated by the Downs and Black checklist showed low and moderate methodological quality (Table 2). The most used instrument to measure spirituality was the Functional Assessment of Chronic Illness Therapy - Spiritual Well-Being - FACIT-Sp^22,25-27, and the numerical scale was used to assess pain^20,27,32. A semi-structured interview was used to assess both spirituality and pain in three studies^24,30,31(Table 2).

The relationship between spirituality and pain was significant in six studies. Nine studies^{21-23,25-28,31,32} showed that spirituality contributes to the positive coping of pain. Only one²⁹ sought correlations between spirituality and pain, but without significant results. Three studies^20,24,30 suggested that the profile of cancer patients with pain who seek spirituality is more related to social class and ethnicity (Table 3).

Due to the heterogeneity of the data, it was not possible to perform quantitative analyzes of the studies. Regarding the level of spirituality, greater spiritual well-being was associated with less pain intensity in three studies. The reduction in pain intensity measured quantitatively by the visual analog scale (VAS) was evidenced only in one study. The two experimental studies^22,27 aimed at showing whether the type of spiritual strategy used would be effective in reducing pain intensity, pointing out that mindfulness and Spiritual Therapy programs, composed of meditation and relaxation, were strategies that promoted pain relief.

In this summary of the literature data on the relationship between spirituality and coping with pain in cancer patients, we sought to analyze spiritual strategies with evidence for pain management in this health condition. Few studies fill this gap, most of them with cross-sectional design and low to moderate methodological quality. However, most authors admit that positive spiritual strategies have a beneficial effect on pain control in cancer patients.

Only three studies showed statistical differences between groups that use spiritual strategies and those that only adopt biomedical behaviors. The lack of homogeneity in the studies prevented the use of metanalysis for their assessment. However, most studies on the topic are still in the observation phase. It is necessary to move towards clinical trials that can test hypotheses in a controlled manner. The few findings, so far, point to promising results for the recommendation of its indication in health services in addition to religious institutions. Meditation practices and body relaxation techniques have been adopted with positive results^9,27,33, even though they lack methodological standardization.

Social class and ethnicity seem to influence the choice of using spiritual strategies to cope with pain in this health condition. Afro-descendant groups have a rich culture of spiritual rites and practices^24,34. However, the lack of education, socioeconomic factors, and the lack of other resources, such as the absence of more potent painkillers due to the high cost, lead these people to seek spiritual strategies as the only alternative. In any case, it is worth mentioning that the lack of alternatives can lead people with cancer pain to find an effective resource to deal with the problem.

Spiritual strategies, such as meditation and relaxation practices, are increasingly common in contemporary health systems. However, people with less education and unfavorable socioeconomic conditions are unaware of these types of services^30,35. It is known that spiritual practice is related to physiological responses in the hypothalamic-pituitary-adrenal axis, by reducing the adrenocorticotrophic hormone and cortisol, and consequently reducing stress, which may be related to pain³⁶.

The choice to use a spiritual activity is very personal and is related to the system of beliefs, values, customs, behaviors, and sociocultural attitudes³⁷. When comparing cancer patients who sought integrative medicine and the inclusion of spiritual practices as part of the treatment with those who did not want this aspect of care, it was found that patients who sought the service for spiritual reasons had more pain, depression, and stress than the other group²⁰. It is possible that, while pain is at the limit of control with other approaches, spirituality is disregarded, only entering the list of choices when the situation is already out of control.

The advanced clinical stage in cancer causes spiritual conflicts³⁸, which naturally leads to the search for spirituality to alleviate this feeling and improve the quality of life³⁹. Spiritual coping strategies have been identified as beneficial for people in pain, being associated with greater tolerance, better mood, and well-being⁴⁰. The findings of the present study confirm the hypothesis that spiritual practices are linked to the search for solutions when ill, in an attempt to relieve the suffering created by the disease, which may be based on their beliefs, regardless of religion; they consider that these strategies are of daily use, such as going to church, relying on family and friends, praying, reading the Bible, among others⁴¹.

Unfortunately, many studies that address the topic have a typical conflict of interest of being carried out by practitioners and leaders of a specific religion or philosophy. Reading religious texts on the “word of God” or specific hymns and cults can create resistance on the part of unbelieving patients or those belonging to a different faith system. Many dogmas can clash with one another. Therefore, spirituality should not be a synonym for religion⁴². Religion is dogmatic; however, aspects such as optimism, hope, resilience, acceptance, among others, are more related to high levels of spirituality. Higher levels of spirituality can be obtained both in religious paths and in spiritual practices^43,44.

Important spiritual strategies were revealed when exploring the relationship of coping with pain through spirituality, the main ones being meditation and relaxation techniques. Spiritual strategies are those activities that seek to strengthen the meaning of life, faith or existential components, peace with oneself, and with others⁴⁵. Patients resort to different practices as needed. However, it is clear that mindfulness, meditation, and prayer are the most used to bring a feeling of comfort and strength⁴⁶.

Meditation is an effective strategy in stressful situations, such as cancer diagnosis and treatment. Among the various techniques, mindfulness stands out, which seeks to concentrate on a reference point through breathing, movements, body sensations, or mantras⁴⁷. A non-randomized clinical trial showed that the use of this meditation was a beneficial strategy to improve spiritual well-being and reducing the intensity of pain²². In addition to meditation itself, relaxation techniques have also been effective in controlling pain in mastectomized women²². The lack of quantification of pain in that study creates an absence of evidence. For this reason, further studies should be conducted to provide the necessary support for the incorporation of this practice by health teams.

In one of the selected studies, cancer patients undergoing mastectomy sought support from religious leaders and members³¹. In India, the lowest income population used firm faith in the doctor, praying, and meditation as a strategy to cope with pain while those with the highest income kept with conventional treatment with the use of drugs³⁰. It is likely that personal belief in an external entity, be it the doctor or God, may favor self-regulatory processes⁴⁸.

Pain is a common physical symptom in cancer patients, which can go beyond the psychosocial dimension. Traditional treatment consists of using analgesic and opioid drugs to relieve physical symptoms, although psychological conflicts are capable of interfering with pain control³⁸. Pain intensity is greater in anguished cancer patients when compared to those who trust in the future and God, corroborating that spirituality is a good mechanism for coping with pain³².

In the case report analyzed²¹, whose goal was to present the integration of spiritual aspects to the health and disease process of a female patient with pancreatic cancer, evangelical and former “mãe de santo” (a religious leader of some African-Brazilian religions) for 27 years. She realized that the use of painkillers, together with reading the Bible, prayer, and meditation, influenced the reduction of pain. The intensity was reduced from level seven to nine to level zero after follow-up. However, the pain returned influenced by the chronic nature of the disease and by the existence of spiritual and family conflicts, after spiritual assistance by a multidisciplinary team. Even so, the pain remained controlled and, later, the patient died calmly and peacefully. Although one case study does not contribute with evidence, they are important as initial exploratory studies that can point the way to prospective studies. Nonetheless, this case represents another confirmation of the impact of spirituality on cancer patients’ pain.

The important limitation pointed out in the present review is directed to the low amount of scientific studies on the theme involving spirituality and pain in cancer patients. Moreover, the methodological quality of most studies was considered low. However, it is worth mentioning that the review strictly followed the current recommendations for the preparation of systematic reviews, which supports the robustness of the results. It is important to carry out new studies with experimental design and representative samples to investigate the effect of spirituality on cancer patients’ pain.