Breast cancer is the second most frequent tumor globally and the most common among women (Andreis et al., Reference Andreis, Meriggi, Codignola, Frigoli, Prochilo, Mutti, Huscher, Libertini, Di Biasi, Abeni, Ogliosi, Noventa, Rota, Pedrali and Zaniboni2018; Ferlay et al., Reference Ferlay, Soerjomataram, Dikshit, Eser, Mathers, Rebelo, Parkin, Forman and Bray2015). Intrusive medical treatments (e.g., chemotherapy and/or radiotherapy) and related side effects lead to physical, psychological, and social long-term impairments (Ahmad et al., Reference Ahmad, Fergus and McCarthy2015; Durosini et al., Reference Durosini, Triberti, Sebri, Giudice, Guiddi and Pravettoni2021; Williams & Jeanetta, Reference Williams and Jeanetta2016). For instance, undesirable physical changes (e.g., loss or deformities in the breast(s), visible scarring, hair loss, and weight fluctuation) promote a negative perception of body image within the bodily self-construct, which is associated with impairments in different aspects of life, like social and work, less physical health, and high levels of psychological distress (Paterson et al., Reference Paterson, Lengacher, Donovan, Kip and Tofthagen2015; Sebri et al., Reference Sebri, Triberti and Pravettoni2021; Durosini et al., Reference Durosini, Triberti, Savioni, Sebri and Pravettoni2022; Fioretti et al., Reference Fioretti, Mazzocco, Pravettoni, Veronesi, Goldhirsch, Veronesi, Gentilini and Leonardi2017; Sebri and Pravettoni, Reference Sebri and Pravettoni2023). In this regard, the most common comorbidities present in breast cancer patients are depression and anxiety (Burgess et al., Reference Burgess, Cornelius, Love, Graham, Richards and Ramirez2005). Similarly, fatigue, sleep problems, and intrusive thoughts about the disease (i.e., fear of cancer recurrence) diminish quality of life (QoL), even some years after successful treatments (Liu, Butow et al., Reference Liu, Wang, Li, Zhao and Li2021a; Sebri et al., Reference Sebri, Durosini, Mazzoni and Pravettoni2022). The World Health Organization (WHO, 2014) defines QoL as the perception and satisfaction with life and their general appraisal of their level of functional well-being. Dealing with chronic disease, it is fundamental to preserve a positive QoL, fostering strategies of functional coping skills. Positive coping skills refer to a person’s cognitive, behavioral, and emotional adjustment to (changing) situations (Folkman & Moskowitz, Reference Folkman and Moskowitz2004). Positive coping skills are relevant also to address the cancer-related fatigue, which is defined as a common and debilitating side effect of cancer pathology and its treatment (Wang et al., Reference Wang, Liang, Lu, Zhao and Zhang2020). Nowadays, the literature demonstrates that several psychological interventions, such as mindfulness and acceptance therapy-based intervention, cognitive behavioral therapy (CBT), psychoeducation, supportive-expressive group therapy, or positive psychology interventions, are beneficial to enhance QoL in breast cancer patients and survivors (Guarino et al., Reference Guarino, Polini, Forte, Favieri, Boncompagni and Casagrande2020). Referring to compassion-based interventions (CBIs), Wispé (Reference Wispé1991) included the ability to adopt a nonjudgmental stance toward others and their sufferings. Reflecting the findings of Wispé, Neff (Reference Neff2003) developed the model of self-compassion, which has been defined as compassion directed inward toward the self. The author reported that self-compassion involves three main components: kindness (being kind toward the self, without self-judgments); mindfulness (holding painful feelings in a mindful awareness); and common humanity (considering people’s suffering as part of the human condition instead of in isolation). Kanov et al. (Reference Kanov, Maitlis, Worline, Dutton, Frost and Lilius2004) argued that compassion involves three facets: noticing (the awareness of a person’s suffering), feeling (the emotional responses to that suffering in an empathic way), and responding (the desire to act to alleviate the others’ suffering). Moreover, a current review by Strauss et al. (Reference Strauss, Taylor, Gu, Kuyken, Baer, Jones and Cavanagh2016) proposed five elements related to a compassion definition: recognizing suffering, understanding the universality of human suffering, tolerating uncomfortable feelings, feeling for people suffering, and motivation to act and alleviate the present suffering. The purpose of CBIs is the cultivation of compassion, and its main components are psychoeducation, reflective compassion exercises, and homework with formal and informal daily life compassion practice (Kirby et al., Reference Kirby2017). Over the years, interest in CBIs has increased significantly also in the healthcare fields (González-Hernández et al., Reference González-Hernández, Campos, Diego-Pedro, Romero, Baños, Negi and Cebolla2021). A review by Austin et al. (Reference Austin, Drossaert, Schroevers, Sanderman, Kirby and Bohlmeijer2021) highlighted the potential benefits of CBIs for people with long-term physical conditions showing improvements in depression, anxiety, and self-compassion and strengthening the mixed-methods approaches based on the integration of qualitative and quantitative findings. Similarly, a meta-analysis by Ferrari et al. (Reference Ferrari, Hunt, Harrysunker, Abbott, Beath and Einstein2019) found moderate effect size for depression (g = 66), anxiety (g = 0.57), stress (g = 0.67) and self-compassion (g = 0.75). Craig et al. (Reference Craig, Hiskey and Spector2020) supported the relevance of CBIs, considering their integrative and holistic approach to universal human suffering, enabling its further adoption into mainstream clinical practice. Referring to breast cancer patients, Przezdziecki et al. (Reference Przezdziecki, Sherman, Baillie, Taylor, Foley and Stalgis-Bilinski2013) stated that self-compassion promotes well-being by mediating the relationship between distress and body image positively. Furthermore, psychological studies evidenced the relevance of recognition and awareness of suffering and emotionally connecting those sufferings with the desire to act to alleviate them (Goetz et al., Reference Goetz, Keltner and Simon-Thomas2010; Jazaieri et al., Reference Jazaieri, McGonigal, Jinpa, Doty, Gross and Goldin2014; Kanov et al., Reference Kanov, Maitlis, Worline, Dutton, Frost and Lilius2004; Lazarus, Reference Lazarus1991). In line with this, literature shows the efficacy of different types of self-compassion interventions. Compassion-focused therapy (CFT) concentrates on helping patients relate to their difficulties in compassionate ways, as well as providing them with effective tools to work with challenging circumstances and emotions they encounter. CFT enriches the compassion-based soothing system while withdrawing from the threat-focused emotional regulation system. In turn, this will augment the ability to address valued goals (Gilbert, Reference Gilbert2009). Another available approach is the Mindful Self-Compassion, which combines the skills of mindfulness and self-compassion, providing a powerful tool for emotional resilience. Randomized controlled trials (RCTs) have demonstrated that Mindful Self-Compassion significantly increases self-compassion, compassion for others, mindfulness, and life satisfaction, as well as decreasing depression, anxiety, and stress (Neff & Germer, Reference Neff and Germer2013). Other approaches include Compassion Cultivation Training (CCT) and Cognitively Based Compassion Training (CBCT). Compassion Cultivation Training is a traditional contemplative practice integrated with contemporary psychology and scientific research. Compassion Cultivation Training provides training in compassion practices in which are involved six stages (Kirby, Reference Kirby2017): (a) settling the mind to develop mindfulness skills, (b) experiencing love, kindness, and compassion for the loved ones, (c) practicing Loving Kindness Meditation (LKM) for oneself, (d) compassion toward others through embracing our shared common humanity, (e) compassion toward all beings, and (f) active compassion practice through imagining taking away others’ pain and offering to them joy and happiness. CBCT incorporates mindfulness and cognitive restructuring strategies to encourage a shift of perspective through reflection regarding social relationships (Reddy et al., Reference Reddy, Negi, Dodson-Lavelle, Ozawa-de Silva, Pace, Cole, Raison and Craighead2013). Moreover, Cultivating Emotional Balance proposes another mindfulness approach focused on recognizing and understanding emotions, also referring to others. It is an educational training to foster people to tolerate distress thanks to new ways of managing emotions (Kirby, Reference Kirby2017). Finally, compassion and LKM involves a structured approach where individuals can learn to direct caring feelings toward themselves, loved ones, acquaintances, and strangers, then toward someone you may experience conflicts or difficulties, and finally toward all living beings (Galante et al., Reference Galante, Galante, Bekkers and Gallacher2014). It is paramount to notice that all CBIs have their specificities in terms of characteristics and aims and in continuous growth. Gilbert et al. (Reference Gilbert, Baldwin, Irons, Baccus and Palmer2006) supported the relevance of self-compassion attitudes too. Specifically, the authors affirmed that feelings of warmth and reassurance for the self could lead to significant reductions in negative emotions (e.g., depression, anxiety, and shame) as well as self-criticism and a sense of inferiority. This way, compassionate mind training may increase well-being in chronic patients, especially those who may lack a sense of inner warmth or ability to self-soothe (Gilbert, Reference Gilbert2010, Reference Gilbert2014). Finally, the meta-analysis by Kirby (Reference Kirby2017) shows significant differences between-group in compassion, self-compassion, mindfulness, depression, anxiety, psychological distress, and well-being, highlighting the associations between the fears of compassion and mental health. However, the authors evidenced the lack of standardization in the current research; indeed, further RCTs are needed to reduce the existing methodological limitations. In the field of breast cancer, in particular, many intervention studies have been conducted. A current meta-analysis by Fan et al. (Reference Fan, Hsiao and Hsieh2023) reported that both online and face-to-face CBI’s enhance overall well-being, increase self-compassion, and reduce depression.

Despite the current literature demonstrates the efficacy of CBIs in chronical fields, there is a lack of knowledge about breast cancer patients and survivors. It is needed to progress scientific investigation by capturing CBIs’ causes and their consequences to make them tailored to breast cancer patients and survivors’ needs. The present systematic review would assess the efficacy of CBIs in this population to highlight key areas of research and clinical practice. It is fundamental to enhance breast cancer patients’ and survivors’ well-being by exploring current studies and conducting an in-depth comparison with other reviews and meta-analyses. This systematic review aims to analyze the efficacy of CBIs on physical and psychological well-being in breast cancer patients and survivors. In particular, we aimed to assess emotions, coping skills, and QoL. Our hypothesis is that CBIs will diminish depression, anxiety and stress and that they will increase positive coping skills in breast cancer patients and breast cancer survivors, thus improving their overall QoL.

2. Methodology

The review question was clearly defined using the Patient, Population, Intervention, Comparison, and Outcome (PICO) strategy. Do breast cancer patients and survivors benefit from receiving CBI’s compared to other active treatments or treatment-as-usual in terms of their depression, anxiety, stress, QoL, and positive coping skills?

2.1 Search Strategy

A systematic search was carried out on ProQuest, Web of Science, Scopus, and PubMed for articles published during the previous 10 years up to November 2023. Gray and peer-reviewed literature were also included. The query string was as follows (compassion* OR self-compassion OR self-kindness OR compassion-based intervention* OR compassion-focused therapy OR mindful self-compassion OR compassion cultivation training OR cognitively based compassion training OR cultivating emotional balance OR compassion and loving-kindness meditation OR compassionate mind training OR metta OR karuna) AND breast cancer AND (RCT). In relation to writing the command line in the different databases, some search filters were taken into account. When writing the query string in the ProQuest database, we used the “anywhere except full text—NOFT” filter to return only titles and articles with the keywords. Regarding the Web of Science, the “Topic” filter was used. With respect to Scopus and PubMed, the “All fields” box was marked. This systematic review followed the preferred reporting guideline for systematic reviews to ensure strictness, replicability, reliability, and accuracy (PRISMA) (Moher et al., Reference Moher, Liberati, Tetzlaff, Altman, Altman, Antes, Atkins, Barbour, Barrowman, Berlin, Clark, Clarke, Cook, D’Amico, Deeks, Devereaux, Kickersin, Egger, Ernst and Tugwell2009). The protocol was registered in Prospero on January 4, 2022.

2.2 Selection Criteria

In order to evaluate the efficacy of CBIs and their main characteristics to promote well-being in breast cancer patients and survivors, the following inclusion criteria based on the PICO framework were considered (a) breast cancer female patients and survivors over 18 years old previously diagnosed with stages I–IV; (b) RCTs using CBI’s; (c) the comparison with other active treatments or treatment-as-usual; (d) studies addressing emotion-related outcomes, such as stress, anxiety, depression, QoL, and positive coping skills; and (e) only English articles in peer-reviewed journals published from November 2013 to November 2023 have been considered.

Studies including patients with severe psychiatric disorders or did not meet the inclusion criteria specified above were criteria for exclusion. We removed duplicates and records that referenced the same paper. Also, studies that did not involve the keywords (compassion, interventions, breast cancer, RCT) were not included.

2.3 Selection of Studies

Three independent investigators (HIDDEN FOR BLINDED PURPOSE) screened all studies obtained from the databases starting from the title and abstract information. Full-text articles were screened for inclusion by (HIDDEN FOR BLINDED PURPOSE), and selection was made according to the inclusion criteria. In the absence of an agreement, other researchers were consulted (HIDDEN FOR BLINDED PURPOSE) in order to reach a consensus.

A total of 197 articles were found from the four databases, and once duplicate ones were removed and additional records identified (n = 3) through other sources, 174 remained to be reviewed. A first screening, in which the title and abstract were analyzed, resulted in a selection of 23 full-text eligible studies. A total of 14 studies were removed for not involving a CBI. Thus, nine studies were analyzed in this systematic review. The search and selection process are illustrated in a flowchart (Figure 1).

Figure 1.

PRISMA flow diagram (Moher et al., 2009).

2.4 Data Extraction

Data were extracted from the included studies by one investigator (HIDDEN FOR BLINDED PURPOSE), and details were entered into a table to include: publication demographics, study design, participant demographics and baseline characteristics, instruments, emotional change interventions, and outcomes, including depression, anxiety, stress, positive coping skills (mindfulness and compassion skills that are helpful to face difficult everyday situations), and QoL. At the same time, for each of the selected studies, the other researchers (HIDDEN Table) in a blinded manner. Inter-rater reliability analysis showed a good agreement between the researchers.

2.5 Data Synthesis

A three-step approach was undertaken for analysis. Initial analysis included cataloguing the emotional change interventions as reflected in the theoretical domains framework. The emotional change interventions were identified and extracted from each study and summarized. The outcomes of each study were evaluated to see whether the emotional change interventions had a significant impact on the main variables, no impact, or no statistically significant change. In order to describe the range of emotional change interventions, a narrative synthesis of included studies and a related table were provided. Findings are reported based on the research objectives and variables of interest in this systematic review.

2.6 Analysis of the Quality of the Studies

The methods of randomization, the assessment criteria, and the critical review form were assessed with the Cochrane Collaboration tool for assessing the risk of bias in randomized trials. The quality of the studies was assessed by (HIDDEN FOR BLINDED PURPOSE) and then contrasted with the other researchers (HIDDEN FOR BLINDED PURPOSE). We rated the following aspects: selection, realization, detection, and management bias. The following bias domains were evaluated: realization bias, detection bias, handling of outcome data bias, reporting bias, confusion bias, selection bias, intervention bias, and attrition bias.

2.7 Review Methods

In this study, we have presented a qualitative analysis of the data extracted from the articles. First, titles and abstracts were screened in order to determine whether they met the inclusion criteria. An article was rejected when the information provided in the abstract did not reach these criteria. In case an abstract could not be rejected clearly, a full-text revision was carried out. Second, full articles were revised to assess eligibility. We collected data according to a list of relevant information about each article: authors, type of sample and size, design of the intervention, objectives, type of compassion intervention, measurement tools, and outcomes. This information was extracted independently and used to fill the table template by the three reviewers (HIDDEN FOR BLINDED PURPOSE) in a blinded manner. The design research column specified whether more than one experimental or control group was used. Results were split into two columns to compare the significant effects of the intervention on the main variables. The first results column was designed for collecting within-group information for the intervention groups. No differences were made according to the different intervention groups found in some studies, as our interest was to study how the compassion component of the intervention influences the dependent variables post-intervention. Those interventions that included a follow-up process were taken note of in the column. A second column for between-group information was designed. It was reported as “no sig. effects” if no significant effects were found. Results were compared among the reviewers, and agreement was reached. Ultimately, the methodological quality was assessed by (HIDDEN FOR BLINDED PURPOSE) and then contrasted independently with the other researchers (HIDDEN FOR BLINDED PURPOSE). Discrepancies were resolved by consensus.

3. Results

3.1 Study Characteristics

There was a total of 813 patients included in the nine studies. They were aged between 18 and 73, with 53 being the average age. The nine studies in this systematic review included CBIs as the primary intervention and assessed their impact on breast cancer patients and survivors. The studies were conducted in the United States, Spain, Iran, and Australia. Control groups included usual care (UC), waiting list controls, and writing expression activities. Samples were from 30 to 304 breast cancer patients and survivors. Six studies included breast cancer survivors, and three studies included breast cancer patients. Regarding breast cancer patients, in Cheung et al.’s (Reference Cheung, Cohn, Dunn, Melisko, Morgan, Penedo, Saisman, Shumay and Moskowitz2017) study, 14% of the patients had stage I breast cancer, 50% had stage II, 28% had stage III, and 8% had stage IV. The stages of cancer were not reported in the studies by Sadeghi et al. (Reference Sadeghi, Yazdi-Ravandi and Pirnia2018) and Wren et al. (Reference Wren, Shelby, Soo, Huysmans, Jarosz and Keefe2019). The study characteristics are shown in Table 1. Compassion interventions ranged from Lessons in Linking Affect and Coping (LILAC), CBCT, My Changed Body (MyCB), CFT, LKM, Self-Compassion-Focused (SCF) to performing acts of kindness, and a self-kindness meditation.

Table 1.

Studies included in this systematic review

Note. Anx = Anxiety; BAI = Beck Anxiety Inventory; BDI = Beck Depression Inventory; BSI-18 = Brief Symptom Inventory; CAMS-R = Cognitive and Affective Mindfulness Scale—Revised; CBI = Compassion-Based Interventions; CES-D = Center for Epidemiologic Studies Depression Scale; DASS21 = Depression Anxiety Stress Survey; DES = Differential Emotions Scale; FACT-B+44 = Functional Assessment of Cancer Therapy– Breast Cancer; FCR = Fear of Cancer Recurrence; FCRI = Fear of Cancer Recurrence Inventory; FFMQ-SF = Five Facets of Mindfulness Questionnaire–Short Form; LILAC = Lessons in Linking Affect and Coping; LKM = Loving Kindness Meditation; M QoLS = Multidimensional Quality of Life Scale; MyCB = My Changed Body; PANAS = Positive and Negative Affect Schedule; QoL = Quality of Life; SCB = Self-Compassion-Based; SCS = Self-Compassion Scale; SF-12 = Medical Outcomes Study Short Form 12-Item Health Survey, the Physical and Mental Health Composite Scores; STAI = State-Trait Anxiety Inventory; Str = stress; AOKO = acts of kindness for others; AOKS = acts of kindness for self; SKM = Self-kindness meditation.

LILAC is a 5-week positive affect intervention of 1-hour sessions to learn eight empirically validated skills: noticing positive events, savoring positive events, gratitude, mindfulness, positive reappraisal, focusing on personal strengths, setting and working toward attainable goals, and small acts of kindness (Moskowitz et al., Reference Moskowitz, Hult, Duncan, Cohn, Maurer, Bussolari and Acree2012). CBCT is an 8-week intervention. Each session comprises 2 hours of didactics, class discussion and guided meditation practice. It includes: (a) developing meditative concentration, (b) mindfulness, (c) causes of suffering and self-compassion, (d) practice in equanimity, (e) practice in gratitude, (f) practice in affection, (g) compassion, (h) happiness, and (i) freedom from suffering (Negi, Reference Negi2013). MyCB is a self-paced writing intervention with a self-compassionate approach. It is evidenced-based and comprises six steps with a duration of about 30 minutes each. It addresses the themes of common humanity, mindfulness, and self-kindness (Neff, Reference Neff2003). MyCB + M: identical to MyCB with the addition of a brief 5-minute self-compassion meditation. Compassion-focused intervention is 16 twice-weekly sessions of 90 minutes each, based on Gilbert’s compassion protocol. LKM is focused on developing positive emotions toward oneself and others. The meditation included a silent repetition of phrases to direct feelings of love, compassion, and gratitude to others (Salzberg, Reference Salzberg2011). The Self-Compassionate Writing Task Intervention includes writing about a negative event and then writing to show understanding and kindness. Its focus is on the self-kindness component of self-compassion and adopting a mindful perspective of the situation.

Most of the interventions were in-person (CBCT, CFT, LKM, and SCF), two online (MyCB and kindness-focused practices), and another blended (LILAC). In most of the studies, the participants were given daily materials to practice. In the LILAC intervention, home practice was high. Participants completed their home practice 5 days per week (Cheung et al., Reference Cheung, Cohn, Dunn, Melisko, Morgan, Penedo, Saisman, Shumay and Moskowitz2017). In the CBCT group, home practice was 3.6 days a week (Dodds et al., Reference Dodds, Pace, Bell, Fiero, Negi, Raison and Weihs2015). In the Gonzalez-Hernandez et al. (Reference Gonzalez-Hernandez, Romero, Campos, Burychka, Diego-Pedro, Baños and Cebolla2018) study, 46.5% of the participants practiced between 4 and 7 days a week. Other studies like the MyCB and self-compassionate writing activities were just single sessions. Follow-up was very different depending on the studies. In the LILAC intervention, follow-up was 77%. In the CBCT groups, follow-up participation was 67% (Dodds et al., Reference Dodds, Pace, Bell, Fiero, Negi, Raison and Weihs2015) and 75% (Gonzalez-Hernandez et al., Reference Gonzalez-Hernandez, Romero, Campos, Burychka, Diego-Pedro, Baños and Cebolla2018). In one of the MyCB studies (Mifsud et al., Reference Mifsud, Pehlivan, Fam, O’Grady, van Steensel, Elder, Gilchrist and Sherman2021), 51% of the participants adhered to the immediate follow-up protocols, and in the other MyCB study (Sherman et al., Reference Sherman, Przezdziecki, Alcorso, Kilby, Elder, Boyages, Koelmeyer and Mackie2018), 50% did so, and 31% completed the 1-month follow-up study questionnaire. Four studies did not collect follow-up measures (Sadeghi et al., Reference Sadeghi, Yazdi-Ravandi and Pirnia2018; Wren et al., Reference Wren, Shelby, Soo, Huysmans, Jarosz and Keefe2019; Przezdziecki & Sherman, Reference Przezdziecki and Sherman2016; Haydon et al., Reference Haydon, Walsh, Fritz, Rahal, Lyubomirsky and Bower2023). Among the studies of this systematic review, positive coping skills were tested in eight studies, seven studies measured depression, four measured anxiety, three measured stress, and three studies measured QoL.

3.2 Data Quality

3.2.1 Risk of Bias Assessment

The Cochrane Collaboration tool was applied to assess the risk of bias (Higgins et al., Reference Higgins, Altman, Gøtzsche, Jüni, Moher, Oxman, Savovic, Schulz, Weeks and Sterne2011). The selection, realization, detection, and management of outcome bias are all assessed in the studies (Figure 2). Regarding selection bias, the randomized sequence generation showed a low risk as they were all randomized studies in which neither researchers nor participants knew which group each participant is assigned to. The allocation concealment had a low risk, as the method of randomization was explained. Only one study did not address this outcome, and so because of that, it is considered “unclear” (Sadeghi et al., Reference Sadeghi, Yazdi-Ravandi and Pirnia2018). Regarding realization bias, the risk of bias was high in two studies as there was no blinding or incomplete blinding, and the outcome was likely to be influenced by a lack of blinding (Cheung et al., Reference Cheung, Cohn, Dunn, Melisko, Morgan, Penedo, Saisman, Shumay and Moskowitz2017; Dodds et al., Reference Dodds, Pace, Bell, Fiero, Negi, Raison and Weihs2015). In one study, there was insufficient information, so it was an “unclear” bias. The rest of the studies were assessed on a low risk of realization bias level. The detection bias was also assessed. The evaluators were not blinded in any studies, but it is considered that the outcome measurements were not likely to be influenced by this lack of blinding. For these criteria, it is considered that all the studies had a low risk of bias. Regarding missing outcome data bias, all studies reported this outcome, or no missing outcome data were reported. For this reason, in seven out of the eight studies, there was a low risk of this bias. There was only one study with insufficient reporting of attrition to permit judgment. For this reason, there is an “unclear” risk of bias (Sadeghi et al., Reference Sadeghi, Yazdi-Ravandi and Pirnia2018). Finally, the bias in reporting the outcome was “unclear” in all nine studies as there was not sufficient information to judge it.

Figure 2.

Graph of the risk of bias.

3.3 Effects of CBIs on Breast Cancer Patients and Breast Cancer Survivors

3.3.1 Depression, Anxiety, and Stress

Depression symptoms were tested in seven studies. In five of them, it was shown to have reduced (Cheung et al., Reference Cheung, Cohn, Dunn, Melisko, Morgan, Penedo, Saisman, Shumay and Moskowitz2017; Dodds et al., Reference Dodds, Pace, Bell, Fiero, Negi, Raison and Weihs2015; Sadeghi et al., Reference Sadeghi, Yazdi-Ravandi and Pirnia2018; Sherman et al., 2018). The Cheung et al. study showed decreased depression (P = 0.03) with an effect size of d = −0.81 at the 1-month follow-up assessment. In the Gonzalez-Hernandez et al. (Reference Gonzalez-Hernandez, Romero, Campos, Burychka, Diego-Pedro, Baños and Cebolla2018) study, it was significant just in the within-group assessment with moderate effect sizes from 0.44 to 0.55. There was no effect in the studies of Haydon et al. (Reference Haydon, Walsh, Fritz, Rahal, Lyubomirsky and Bower2023) and Mifsud et al. (Reference Mifsud, Pehlivan, Fam, O’Grady, van Steensel, Elder, Gilchrist and Sherman2021). Depression showed a significant Time × Group effect evidencing lower levels at post-intervention in those interventions that used CBCT (−3.7, 95% CI −6.3, −1.1) and CFT (p < .001) conditions compared with a waitlist group and a motivational enhancement therapy (MET), respectively (Dodds et al., Reference Dodds, Pace, Bell, Fiero, Negi, Raison and Weihs2015; Sadeghi et al., Reference Sadeghi, Yazdi-Ravandi and Pirnia2018). Haydon et al. found that performing kindness-focused practices did not produce any statistically significant decrease in depression levels compared to daily activity writing. Intragroup analysis showed significant reductions in depression at post-intervention and follow-up after receiving LILAC (P = 0.03, d = −0.81), CBCT, and CFT interventions. Anxiety was tested in five studies (Mifsud et al., Reference Mifsud, Pehlivan, Fam, O’Grady, van Steensel, Elder, Gilchrist and Sherman2021; Sadeghi et al., Reference Sadeghi, Yazdi-Ravandi and Pirnia2018; Sherman et al., Reference Sherman, Przezdziecki, Alcorso, Kilby, Elder, Boyages, Koelmeyer and Mackie2018; Wren et al., Reference Wren, Shelby, Soo, Huysmans, Jarosz and Keefe2019). Similarly, significant Time × Group interactions were seen for anxiety showing significant reductions at post and follow-up after receiving CFT (p < .001), LKM (p = .05), and MyCB (F(2, 23) = 8,12, p = .002) compared to expressive writing, MET and music or UC, respectively (Sadeghi et al., Reference Sadeghi, Yazdi-Ravandi and Pirnia2018; Wren et al., Reference Wren, Shelby, Soo, Huysmans, Jarosz and Keefe2019; Mifsud et al., Reference Mifsud, Pehlivan, Fam, O’Grady, van Steensel, Elder, Gilchrist and Sherman2021). Stress was measured in three studies. Dodds et al. (Reference Dodds, Pace, Bell, Fiero, Negi, Raison and Weihs2015) found significant reductions (−1.6, 95% CI −3.1, −02). Also, in the study by Gonzalez-Hernandez et al. (Reference Gonzalez-Hernandez, Romero, Campos, Burychka, Diego-Pedro, Baños and Cebolla2018), stress was reduced (0.68, 95% CI −0.36, 1). No effects on stress were found in the study by Mifsud et al. (Reference Mifsud, Pehlivan, Fam, O’Grady, van Steensel, Elder, Gilchrist and Sherman2021). Also, significant Time × Group effects were shown for stress at post-intervention and follow-up after receiving CBCT (F (2, 96.863) = 3.521; P < 0.05) compared to TAU (Gonzalez-Hernandez et al., Reference Gonzalez-Hernandez, Romero, Campos, Burychka, Diego-Pedro, Baños and Cebolla2018).

3.3.2 Quality of Life

QoL was tested in three studies (Dodds et al., Reference Dodds, Pace, Bell, Fiero, Negi, Raison and Weihs2015; Gonzalez-Hernandez et al., Reference Gonzalez-Hernandez, Romero, Campos, Burychka, Diego-Pedro, Baños and Cebolla2018; Haydon et al., Reference Haydon, Walsh, Fritz, Rahal, Lyubomirsky and Bower2023). In the study by Gonzalez-Hernandez et al., within-group comparisons revealed a significant post-intervention increase in the CBCT intervention with a moderate effect size (d = 0.75) when compared to TAU and when comparing acts of kindness to daily activity writing (p = .002, 95% CI [0.67, 2.95]).

3.3.3 Positive Coping Skills

They were tested in eight studies. The study by Cheung et al. (Reference Cheung, Cohn, Dunn, Melisko, Morgan, Penedo, Saisman, Shumay and Moskowitz2017) found only marginal increase in positive coping by 1 month FU (P < 0.08) with medium to large effect size (0.50 < d > 0.91). Dodds et al. (Reference Dodds, Pace, Bell, Fiero, Negi, Raison and Weihs2015) found after week 8 that CBCT had enhanced mindful presence (3.6, 95 % CI 1.2, 6.0). After week 12 they found a significant mindful presence (3.1, 95 % CI 0.4, 5.8). They also found significant differences in time × group interaction at post and follow-up for self-kindness (P < 0.05; d = 0.94; 95% CI = [0.34, 1.55]. Within-group analyses showed significant pre-to-post changes for self-kindness, identification, and self-compassion. The mindfulness facets of observing F[2, 96.052] = 4.709; P < 0.05) and awareness (F[2, 98.598] = 3.444; P < 0.05) showed significant time × group interaction. Within-group comparisons revealed a significant pre-post change for the skill of observing in the CBCT intervention, with a large effect size (−0.86). In the study by Wren et al. (Reference Wren, Shelby, Soo, Huysmans, Jarosz and Keefe2019) treatment × time interaction was significant for self-compassion [F(2, 41) = 4.51, p = .02]. It increased over time (p = .001, 95% CI = 0.07, 0.25). In the study by Przezdziecki and Sherman (Reference Przezdziecki and Sherman2016), post-writing scores increased for self-compassionate attitude, F(1, 105) = 4.87, p = .03 with a small effect size of 0.26. Moreover, in reference to emotion-related outcomes, Gonzalez-Hernandez et al. (Reference Gonzalez-Hernandez, Romero, Campos, Burychka, Diego-Pedro, Baños and Cebolla2018) reported an open manner of relating to oneself during difficult situations is a helpful coping strategy that increases emotional well-being. Similarly, functional coping strategies have a clinical utility by improving positive emotions and encouraging self-compassionate attitudes after experiencing a negative event (Mifsud et al., Reference Mifsud, Pehlivan, Fam, O’Grady, van Steensel, Elder, Gilchrist and Sherman2021).