Positive Psychology Approaches to Interventions for Cancer Dyads: A Scoping Review

Objective: Positive psychology approaches (PPAs) to interventions focus on developing positive cognitions, emotions, and behavior. Benefits of these interventions may be compounded when delivered to interdependent dyads. However, dyadic interventions involving PPAs are relatively new in the cancer context. This scoping review aimed to provide an overview of the available research evidence for use of dyadic PPA-based interventions in cancer and identify gaps in this literature. Methods: Following PRISMA guidelines, we conducted a scoping review of intervention studies that included PPAs delivered to both members of an adult dyad including a cancer patient and support person (e.g., family caregiver, intimate partner). Results: Forty-eight studies, including 39 primary analyses and 28 unique interventions, were included. Most often (53.8%), the support person in the dyad was broadly defined as a “caregiver”; the most frequent specifically-defined role was spouse (41.0%). PPAs (e.g., meaning making) were often paired with other intervention components (e.g., education). Outcomes were mostly individual well-being or dyadic coping/adjustment. Conclusions: Wide variability exists in PPA type/function and their targeted outcomes. More work is needed to refine the definition/terminology and understand specific mechanisms of positive psychology approaches.


Introduction
Nearly 40% of men and women will be diagnosed with cancer during their lifetimes [1]. Many of these individuals receive substantial, unpaid, support from an informal caregiver, often a family member or friend. Both patient and caregiver psychological and physical health have been shown to be impacted by cancer, and importantly, many studies have documented the interdependence of psychological and physical outcomes in patients and their caregivers [2,3]. Traditionally, psychosocial and behavioral interventions to improve patient and caregiver health have been targeted toward the individual [4,5]. However, because of the interdependence between patients and caregivers [6], research has espoused the benefits of dyadic behavioral interventions to support well-being. In these interventions, two people-often the person with cancer and their caregiver-are active participants in the intervention. Findings suggest the dyadic approach is effective for improving well-being, including depression, anxiety, and quality of life [7,8].
Many existing psychosocial interventions, including those developed for dyads, are pathology-and deficit-oriented. Positive psychology offers a re-orientation to this approach, as it is a field of psychological theory and research that focuses on the psychological states, individual traits, and social institutions that enhance subjective well-being [9]. As such, interventions that are based on or incorporate aspects of positive psychology (from here on referred to as positive psychology approaches, or PPAs) aim to supplement the traditional purpose. Interventions that are primarily mindfulness-based (e.g., mindfulness-based stress reduction/MBSR) or interventions that include mindfulness along with other PPA-based components were included, as mindfulness is linked to the positive psychology pillar of positive emotion, and mindfulness is often considered a tool of positive psychology [27].
We excluded studies that focused primarily on activities-based interventions that are not explicitly rooted in positive psychology, including yoga or other physical exercises for purposes of promoting well-being, relaxation and imagery/visualization exercises, art therapy, and music therapy. We also excluded interventions that do not have a primary focus on at least one of the five pillars of positive psychology, including behavioral activation, psychoeducational interventions, cognitive behavioral therapy, cognitive therapy, cognitive behavioral stress management, acceptance and commitment therapy, dialectical behavior therapy, problem-focused therapies, psychodynamic therapy, and supportiveexpressive therapy.

Information Sources and Search Strategy
Our team developed a list of search terms (See Supplemental Tables S1 and S2) based on our definition of PPAs. A detailed and systematic search was conducted between May 2019 and September 2021 using a combination of free-text-keywords, MeSH, and database-specific controlled vocabulary within PubMed.gov, EMBASE, and Central (Cochrane Library). Search results were downloaded in RIS format from each database/website and imported into an EndNote library. Once compiled into the library, search results were deduplicated three times, once using EndNote, once upon uploading into Covidence (Veritas Health Innovation), and finally once during the title and abstract screening process. Backward searches were conducted using citations in reviews and meta-analyses identified in our initial search until no additional relevant articles were found. Two reviewers were used at each stage of screening (i.e., title and abstract screening, full-text screening).

Eligibility Criteria
See Supplemental Table S3 for a detailed description of inclusion and exclusion criteria. We searched for studies related to PPAs, as described above, delivered to adult dyads comprised of a cancer patient/survivor and one member of the survivor's informal social support network (i.e., family member or friend). We stipulated that the intervention must be delivered to both members of the dyad together for at least part of the intervention, although the intervention did not have to place equal emphasis on both dyad members. For example, the intervention could be delivered to patients individually for most sessions and to the dyad together for a smaller portion of the sessions, and/or outcomes did not have to be assessed or analyzed for both dyad members (e.g., analyses could focus exclusively on patient outcomes). (See the Discussion section below for additional discussion on the variety of ways that "dyadic" may be interpreted in this context.) English-language peer-reviewed articles reporting results of original research-e.g., pilot trials, randomized control trials, and secondary analyses-were included. Articles were not excluded based on publication date. Articles which merely described a study protocol or intervention and did not report results were excluded, such as published and unpublished protocols, methodology write-ups, and guideline reports. Case studies and non-peer-reviewed theses, dissertations, and book chapters were also excluded. Metaanalyses and reviews were not included, but their reference lists were hand-searched to find relevant articles that may have been missed in our database searches.

Study Selection Process
The screening and review process followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines (http://www.prisma-statement.org/, accessed on 14 January 2022). See Figure 1 for the PRISMA flow diagram. A total of 3316 articles were identified through the database search, with an additional 10 articles identified via hand search (3326 total). From these, 232 duplicates were removed, re-
The FOCUS intervention was published on by far the most frequently, with 11 studies (22.9% of 48 included studies, including three secondary analyses) assessing variations of the intervention: brief/extended versions, self-managed web-based versions, and a group-based version. COPE and DYP were the only other interventions included in more than two papers. Intervention was feasible and all participants perceived the program as useful and beneficial; no statistically-significant improvements for PTs or CGs, but clinically-significant improvements seen in cancer-related symptoms, sleep disturbance, depression symptoms, and mental QOL for PTs, and in mental QOL for FCGs; however, a marginally-significant increase in depression symptoms was seen in CGs  the table are Table S4 for demographics of each sample.
There was substantial variation in how the non-patient dyad member was defined. In 21 of the 39 primary studies (53.8%) this dyad member was classified under a general "caregiver" label, which was defined in a variety of ways and sometimes not at all; however, by far the most common type of caregiver was the patient's spouse/partner, with an average of 71% of participating caregivers being the patient's spouse/partner, across studies that reported this information. Study inclusion criteria for caregiver participants varied by time (e.g., time living together, times visited patient), relationship type (e.g., friend, family), or by who "provided the most care" to the patient. Sixteen primary studies (41.0%) specifically recruited patients' spouses/partners (vs. "caregivers" defined more broadly), which varied in including/excluding same-sex partners. The studies that specifically enrolled spouses/partners almost exclusively dealt with breast and prostate cancer. Table 2 contains a summary of each intervention's structure and content, as well as relevant pillar(s) of positive psychology. Although the term "positive psychology" was explicitly mentioned in relation to only one intervention in this review (CBM [41]) aspects of positive psychology were found throughout the descriptions of interventions: Each intervention included a primary focus on activities relevant to at least one and up to four of the five positive psychology pillars. Most commonly, interventions included components related to the positive emotions pillar (n = 20 of 28 unique interventions, 71.4%); in this review, we further categorized positive emotion components into those focused on mindfulness, present in 10 interventions (38.5%), optimism/hope, and other/general positive emotions, both in six interventions (23.1%). Meaning-making and positive relationships were also commonly-represented pillars, each in 11 interventions (39.3%). Activities related to engagement and accomplishment pillars were less common, each in two interventions (7.7%). Beyond CBM [41], which was explicitly informed by positive psychology processes, no intervention was exclusively composed of PPAs. Rather, aspects of positive psychology were included with other dyadic intervention components such as education, managing symptoms, coping, and intimacy.

Outcomes Assessed
Given the relative novelty of dyadic interventions in cancer using PPAs, it is not surprising that many studies focused on feasibility, acceptability, or satisfaction of study components (n = 19 of 48; 39.6%) as primary outcomes. However, a broad range of psychosocial constructs were also assessed as primary outcomes (see Table 1). The most common outcomes were quality of life (n = 27 of 48; 56.3%), depression (n = 14; 29.2%), and anxiety (n = 10; 20.8%), though a variety of unique measures were used to assess these constructs. Overall patterns of results suggest trends towards intervention effectiveness in improving quality of life and reducing depression and anxiety in at least one member of the dyad. Other constructs were too infrequently assessed to make generalities about effectiveness.      Seeks "to empower dyads to cope with cancer and cancer treatments using two major processes from the social problem-solving literature: Problem orientation and problem-solving skills. An optimistic approach to managing the problem and permission to be creative was reinforced throughout the session" (p. 4). [USA]

Discussion
This scoping review highlights the current research on positive psychology approaches (PPAs) in dyads coping with cancer. Findings show that dyadic interventions using PPAs are increasingly used in oncology, particularly as part of multi-component interventions. Interventions were delivered over multiple sessions by an interventionist either to individual dyads or to dyads within a group context. Interventions targeted a wide variety of cancer patients, across both disease site and trajectory, and the type of dyad partner also varied; while many dyads included the patient's spouse or partner, most studies included a broadly-defined "caregiver." The primary outcomes assessed in these interventions were individual psychological well-being and quality of life or distress (including anxiety and depression), dyadic coping or adjustment, and, less often, physical symptoms such as fatigue or pain. This spectrum of intervention participants and targeted outcomes speaks to the flexibility and potential broad application of PPAs, especially as part of a multicomponent intervention.
This review found a variety of activities relevant to positive psychology were used in interventions. Activities were most commonly focused on pillars of positive emotion-especially mindfulness, and optimism or hope-as well as meaning-making and positive relationships. These constructs are particularly well-suited for dyadic interventions in oncology. First, mindfulness, hope, and meaning-making can all be helpful coping tools for cancer patients and their family caregivers [77][78][79][80][81][82]; these cognitive strategies may be especially useful in oncology settings where individuals may feel they have little control over the cancer. Dispositional optimism also has important impacts on symptom experience and quality of life for cancer patients [83] and all-cause mortality more broadly [84]. Cancer has long been viewed as a "family disease"; patients often include family members in decision-making and increasingly rely on caregivers, especially as their health declines [85,86]. This, combined with the benefits of social support in cancer [87,88], means that the oncology setting may especially lend itself to dyadic interventions and a focus on positive relationships.
While the breadth of activities within PPAs demonstrates the wide applicability, similar to previous reviews [14,22], we find this can also create difficulties in pinpointing specific benefits. Since many existing interventions include PPAs as one component among several others (e.g., education, problem-solving, social support), it is difficult to evaluate what may be driving the effects of a given intervention. Some PPAs may also serve as multipliers for the effects of more traditional intervention tools. For example, mindfulness exercises may help participants to focus, reducing anxiety and making problem-solving or education more effective. Finding meaning in their experience may give dyads a deeper well of resilience to draw from when coping with the stresses of cancer. However, particularly because most interventions identified in our search were multi-component, more work is needed to identify mechanisms and determine which specific PPAs are most effective for whom and in which situations. Similarly, when multiple PPAs are employed in a study, it may be beneficial to disentangle how those work together in different contexts to affect key outcomes.
Similarly, other researchers have called for more work to better understand how, why, and for whom dyadic interventions specifically are effective [7]. PPAs typically target the individual, and much of the empirical research supporting the effectiveness of PPAs is based on individual participants, not dyads. It is undeniable that the dyadic aspect of an intervention adds another dimension, which should also be considered in identifying mechanisms. The high level of interdependence of mental and physical health between cancer patients and their family caregivers or spouses, who often participate in dyadic studies, may mean that independent effects are compounded, plus there may be additional unique dyadic effects [6,23]. For example, a gratitude activity between partners may enhance positive emotion and feelings of connectedness in the dyad, which could promote coping with cancer-related stress.
Though many of the studies included in this review focused (appropriately) on feasibility and acceptability, there remains a need to identify which outcomes are most appropriate to measure as key intervention targets. Our review suggests that dyadic interventions with PPAs may be beneficial in terms of quality of life, depression, and anxiety, yet there is no consensus around other constructs that may be impacted, or how to measure these constructs. More work mapping out mechanisms and outcomes to a conceptual model and testing these theories can be beneficial in moving the field forward. Further, using validated measures that allow for data harmonization will be important for future meta-analyses.
Although all interventions in this review included dyads, not all interventions were purely dyadic. In several interventions, some sessions were targeted specifically for patients and included both patient and their dyad partner only in select sessions. For example, the QOL intervention [30] held six sessions for patients, and caregivers were invited to four of these sessions deemed most relevant to both patients and caregivers. Other interventions were delivered to both dyad members, but either due to the specific activities selected or the design of the intervention, maintained an individual focus. Examples include the TSM intervention [34,71], in which both the patient and partner were coached in relaxation exercises, and the COPE intervention [32,45,46], in which both patient and partner were provided guidance in maintaining an optimistic outlook for themselves. This contrasts with other, more truly dyadic, interventions in which dyads participate in activities together and the focus is more on the interaction or interdependence of activities. For example, the ECG intervention [52] included a "wish list" of positive acts each spouse could do for the other and leveraged support to make changes and increase intimacy. Similarly, the FOCUS intervention [55,57,59] included brainstorming positive activities to do together and relies on family strengths. Many interventions also included a hybrid model of both individual and dyadic targets, which may be an ideal strategy to leverage the benefits of interdependence. Additional research is needed to identify benefits to different levels of dyadic inclusion across different activities and interventions.

Limitations and Future Directions
It is well-documented that recruitment and retention of dyads in cancer research is challenging, particularly in advanced cancer contexts. Interventions in our review targeted dyads across the cancer trajectory from diagnosis to end of life. While interventions were largely feasible and offered benefits across this trajectory, most studies in our review were relatively small, and most of their findings have not yet been replicated. Further, the majority of studies sampled patients and caregivers who were mostly White, relatively highsocioeconomic status, and from the US or other Western countries, and spouses/partners were by far the most common type of dyad partner (vs. adult children, siblings, etc.) represented in these studies (see Table 1 and Supplemental Table S3). It is unclear how selection bias may impact the uptake and effectiveness of these interventions. Future research with larger, more diverse samples is needed.
Additionally, although (by design) all interventions in this review targeted dyads-a cancer patient and a partner-the specific role or relationship of the partner may vary (and in some cases, was not clearly defined). For example, some studies focused specifically on romantic partners, while others focused on primary caregivers. These two roles may be taken on by the same individual (i.e., a romantic partner might also be the primary caregiver), but there is certainly some variability-caregivers may also be adult children, siblings, or others, and some romantic partners may also not be highly involved in providing care for the cancer patient. This variability needs additional exploration.
Finally, our review may be limited by a lack of consistent terminology and a consensus definition of "positive psychology approaches" or "positive psychology interventions" [14,22]. Only one intervention was explicitly based in positive psychology, though all included PPAs. This lack of specificity may arise from the relatively recent developmental history of positive psychology [89], which was born from Martin Seligman's theme during his American Psychological Association presidency to more broadly consider the full human experience as being both negative and positive, and to therefore encourage the latter (as well as consider the former). This called for the integration of positive psychology into existing practice, as opposed to establishing a singular approach. As such, there is not yet a clear, widely-accepted set of specific key words to identify these studies, and some dyadic PPAs may not have been identified in this scoping review. We found PPAs in interventions developed across disciplines, including nursing, social work, and palliative care. This demonstrates the broad appeal of these tools, yet also may contribute to the challenges of finding a shared terminology across fields of study.
A multidisciplinary consensus group to begin creating more solid definitions and key terms may be an important step for the growth of this field. Based on our findings-as well as previously-conducted systematic reviews on positive psychology interventions-we propose the following definition: Positive psychology approaches include any intervention that contains in part or wholly aspects of positive psychology theory (e.g., PERMA) to build on recipients' strengths, resources, and values, and whose primary goal is to increase positive feelings, cognitions, and/or behavior, which may be the sole goal of the intervention or in addition to more traditional symptom amelioration.

Clinical Implications
Identifying mechanisms and key components to interventions is important for future dissemination and implementation research. Most interventions in this scoping review involved multiple sessions and many were delivered by highly-trained interventionists, such as nurses, social workers, and clinical psychologists. Understanding the specific components driving effects can help reduce resources needed to deliver interventions and may facilitate translation to alternative delivery systems (e.g., virtual or mHealth). Research supports that mHealth-delivered PPAs can be effectively applied to increase wellbeing and decrease depression across various populations [90,91]. Several interventions identified in our review included a phone or web-based delivery method (e.g., [65,75]), which can facilitate access to a population that is remotely located, may have mobility or transportation issues, or who simply do not have time or energy to convene for programs.
Clinicians should note that positive psychology offers useful, relatively simple approaches to improving quality of life that can be implemented alongside other approaches, such as education. Given the feasibility of dyadic PPAs, as well as the potential for synergistic effects on well-being, clinicians can also consider including caregivers or other supportive individuals in psychosocial assessments and when offering psychosocial resources, including those that include PPAs.

Conclusions
Positive psychology approaches hold promise to have large impacts on improving psychosocial outcomes for those coping with cancer. Further, dyadic PPAs can offer benefits to individuals, but these benefits may be compounded within dyads due to interdependence effects and partner influence. Given the high levels of anxiety and depression that are often reported in both patients and partners coping with cancer, dyadic PPAs may be important tools to improve quality of life. However, to date, the types of positive psychology-based activities that have been delivered in dyadic interventions are highly variable. More work is needed to develop terminology and understand specific mechanisms to develop this area of research and fully appreciate the potential benefits of these tools.

Supplementary Materials:
The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/ijerph192013561/s1. Author Contributions: All authors affirm that all authors made substantial contributions to the conception and design of the work, the screening and review process, and interpretation of findings; drafted or critically revised this work for important intellectual content; approved this work for publication; and agree to be accountable for all aspects of the work. All authors have read and agreed to the published version of the manuscript.