In Europe, 5.4 million women were living with breast cancer in 2020 [1]. In France, more than 61,000 new cases are diagnosed every year, half of them in women of working age [2]. More than 254,000 patients diagnosed with breast cancer in the past 5 years are still alive [3]. While the incidence of breast cancer continues to rise, especially among women under the age of 50 years [4], the retirement age continues to increase. Consequently, returning to work (RTW) after breast cancer is essential for women wishing to resume a professional life [5], ensuring their financial independence and social participation while reducing the social costs associated with the disease [3].

However, research has identified several obstacles that impede women’s RTW [6,7]. These obstacles are associated with the consequences of the disease and its treatment (fatigue, pain, and cognitive problems) and the age of the patients [8,9]. Interprofessional collaboration could effectively support these patients in the postcancer phase, but barriers continue to hinder collaboration between breast cancer specialists, general practitioners, and occupational physicians [10]. In the work environment, professional demands may not be compatible with the patients’ situations. Moreover, a lack of knowledge about the disease, along with insufficient support from superiors and colleagues, may complicate RTW [11,12]. Sociodemographic inequalities also influence RTW, with a less favorable occupational prognosis in older and less-qualified people [13,14].

The importance of RTW has been formalized in France’s 10-year cancer strategy for 2021 to 2030 [15]. Employers are implementing measures to support employee reintegration, including the “Cancer and Employment” charter established by the French National Cancer Institute. The charter seeks to provide additional assistance for individuals undergoing or recovering from cancer treatment [16].

Multidisciplinary interventions appear to increase the number of people who RTW [17]. These interventions are filling the gaps left by overly medicalized interventions, which have been criticized for their weak theoretical basis. Such a basis has proved insufficient for analyzing the causes (problem theory) of obstacles and for proposing solutions (action theory) [18,19].

The Facilitating and Sustain the Return to Work After Breast Cancer (FASTRACS) research program [20] was developed using the intervention mapping framework [21]. It addresses the need for multidisciplinary interventions [22] by engaging various RTW stakeholders early in the cancer care process. The intervention consists of an RTW pathway for breast cancer survivors (BCSs) that connects the hospital, the primary care team, and the workplace environment, starting when active treatments have concluded [20]. This pathway is structured around 4 tasks for supporting BCSs:

With these tasks completed, BCSs can anticipate the potential professional challenges associated with RTW and optimize their comeback.

However, the process of change cannot rely on women alone and must target the behaviors of other stakeholders as well (eg, general practitioners, occupational physicians, managers, and so on), in line with the recommendations on complex interventions [24]. Four tools have thus been developed to facilitate the process, mobilizing the key actors in the RTW process:

A randomized controlled trial (RCT) is currently underway (FASTRACS-RCT, NCT04846972) in 14 investigation centers. The trial will evaluate the effects of the FASTRACS intervention on the sustainable RTW of BCSs 12 months after the end of active treatment [25].

RTW interventions are considered complex interventions due to the diverse influencing factors, the multiple actors involved, and the variety of implementation contexts [26]. Such interventions have a heightened risk of failure in terms of delivery and sustainability due to the dynamic interactions among their components. To better anticipate these challenges, the Medical Research Council recommends evaluating these interventions to gain a contextualized understanding of how they induce changes while analyzing the factors that facilitate or hinder their delivery [26].

Therefore, in addition to conducting a quantitative evaluation of the effects, it is necessary to evaluate the intervention processes [27]. This process evaluation serves 3 key purposes: it provides a dynamic analysis of the intervention’s implementation, examines the mechanisms through which it generates impact, and identifies the contextual factors that influence these mechanisms.

The main objective of the RECOVA-FASTRACS (Realist Collaborative Evaluation of a Work Disability Prevention Program for Breast Cancer Survivors) study is to conduct a process evaluation of the FASTRACS intervention by examining its implementation, context, and impact mechanisms. More specifically, this ancillary study will assess what has been implemented and how, while identifying barriers and facilitators influencing the implementation of the intervention components. In parallel, the context analysis will explore how specific contextual factors affect the intervention’s implementation and outcomes. Finally, the study of impact mechanisms will examine how the intervention produces the expected effects and any unintended consequences that may arise.

The secondary objective is to refine the initial propositions of intervention theory by confirming or revising them through the elaboration of middle-range theories.

Process evaluation can be carried out using various methodological approaches. Among these, realist evaluation [30,31] stands out for its systematic approach to the interactions between intervention and context. Stemming from the theory-based evaluation movement [32], realist evaluation aims to answer the question of “what works, how, why, for whom, and in what circumstances” [30] by identifying context-mechanism-outcome (CMO) configurations. By analyzing these configurations together, researchers can define “demi-regularities” and develop middle-range theories that explain the variations in observed effects [33]. By comparing these theories with the intervention’s initial assumptions in the theory of intervention, the researcher can refine the intervention theory. Applying this approach to the FASTRACS intervention makes it possible to dynamically analyze its implementation and impact mechanisms, supporting its future adaptation and scalability in real-life settings.

RECOVA-FASTRACS is a realist process evaluation conducted as a mixed methods ancillary study to FASTRACS-RCT to refine the initial program theory (publication forthcoming and Broc et al [23]). In this study, the mixed methods approach refers to the integration of qualitative and quantitative data within the overarching realist evaluation framework. It uses a convergent design within a case-study framework [34]. The study integrates theory-testing interviews through a multiple-case study with quantitative data from FASTRACS-RCT using an embedded approach to triangulate findings.

The qualitative research will be divided into 2 parts:

In substudy A, we will analyze the trajectories of RCT-I, focusing on participants’ experiences of the intervention through their own narratives. These results will then be triangulated with those of the people who contributed to their RTW pathway. Data will be collected through semistructured interviews scheduled at the end of the RCT-I follow-up in FASTRACS-RCT to prevent contamination risks.

Simultaneously, substudy B will explore how professionals deliver the intervention. We will conduct focus groups to gather multiple perspectives, allowing for interaction on the topics discussed. This approach will facilitate the identification of organizational dynamics and professional practices specific to each professional [35].

In quantitative research (substudy C), we will analyze data from the RCT questionnaires completed by RCT-I.

Only participants from the intervention arm will be included in the qualitative trajectory analysis, as the objective of the realist evaluation is to explore the implementation processes, mechanisms, and contextual conditions associated with exposure to the FASTRACS intervention. The study does not aim to qualitatively compare intervention and usual-care trajectories. However, experiences related to usual care, RTW barriers, and the ordinary experience of living with breast cancer and RTW have already been extensively explored during the needs assessment phase of the intervention mapping process [20]. In addition, the profession-specific focus groups conducted with professionals involved in RTW support will contribute to documenting routine professional practices and usual-care conditions experienced by women participating in the FASTRACS-RCT. Quantitative data from the FASTRACS-RCT, including participants from both intervention and usual-care groups, will further support contextualization and interpretation of the intervention-specific mechanisms identified through the realist analysis.

Triangulation of qualitative findings with quantitative data will allow the formulation of hypotheses on the implementation, underlying contexts, mechanisms, and effects that the intervention might produce on the RCT-I. Figure 1 illustrates the design of the study.

The realist analysis will be carried out in an extended context-mechanism-outcome configuration: ICAMO [41]. The intervention is defined as the resources and components delivered by the program (eg, patient guide, checklists, and coordination procedures). Context refers to external and individual conditions shaping the activation of mechanisms, including organizational settings, health care pathways, workplace environments, interpersonal relationships, and personal circumstances embedded within different ecological levels of the patient’s situation [42,43]. Actors are individuals or groups whose behavior or reasoning is targeted by the intervention [44]. Mechanisms are defined as changes in reasoning and reactions that bring about change [45]. Outcomes refer to the observable effects generated by these mechanism-context interactions [46].

To avoid any confusion between intervention components and mechanisms, a structured decision rule will be applied during analysis: (1) if a statement describes “what the program provides,” it will be coded as intervention; (2) if it describes “what is happening in the environment,” it will be coded as context; (3) if it describes “what actors think, decide, or do in response to resources within a context,” it will be coded as mechanism.

For example, the patient guide is an intervention component; being provided with the guide is the intervention exposure; feeling reassured or legitimized to discuss RTW with health care providers after reading it is a mechanism; and organizational support from an employer facilitating reduced working hours is a contextual condition influencing whether this mechanism is activated.

A 2-phase thematic analysis of qualitative interviews:

To enhance rigor, at least 2 researchers will independently analyze the transcripts before engaging in counterfactual reasoning and judgmental rationality, comparing and refining the ICAMO configurations. MAXQDA 24 software (MAXQDA) will be used to integrate and compare the entire corpus.

Quantitative data from FASTRACS-RCT surveys (collected at baseline, 4, 8, and 12 mo) will be analyzed following the prespecified statistical analysis plan [25]. In addition, subgroup analyses (eg, by socioprofessional category, age, center, and company size) will be used to test the hypotheses developed during the interviews.

Qualitative and quantitative data will be analyzed in parallel and will be integrated sequentially [47]. For each RECOVA-BCS, qualitative data will be directly embedded into their corresponding quantitative dataset (Multimedia Appendix 2), which includes selected variables from the RCT, such as sociodemographic characteristics (age, occupation, company size, geographical area), RTW outcomes, care pathway indicators, and the use and perceived usefulness of intervention tools. This embedding will allow within-case comparisons and exploration of how qualitative findings relate to quantitative patterns.

Where findings converge, they will be used to strengthen the interpretation of emerging ICAMO configurations. In cases of divergence between qualitative and quantitative data, these discrepancies will be systematically documented and explored as potentially informative for refining the program theory (eg, revealing contextual contingencies or alternative mechanisms).

Integration will be conducted at the analysis level through the use of structured matrices and joint displays [47], which will allow visual and analytical comparison of qualitative and quantitative findings across cases. These tools will also be used iteratively to identify areas of convergence and divergence between datasets. Importantly, this ongoing integration will inform subsequent data collection by highlighting aspects that appear underexplored in qualitative interviews but are emerging from quantitative patterns, thereby guiding the development of additional or more focused interviews to further investigate these discrepancies.

This embedded analysis will allow for constant iteration between empirical observations and the initial program theory, progressively defining middle-range theories that hypothesize for whom, how, and under what conditions the intervention works.

Figure 2 illustrates the realist evaluation of the FASTRACS intervention processes.

The analysis will be led by an interdisciplinary team with expertise in general and occupational medicine, oncology, occupational health, social psychology, and public health. It will be enriched by the Intersectoral Strategic Participatory Committee, which includes 35 stakeholders (patients, associations, employers, professionals, and institutional representatives) involved throughout the project. The committee will contribute to interpreting findings and ensuring their relevance, feasibility, and potential for scale-up.

A study timeline summarizing recruitment, qualitative and quantitative analyses, focus groups, mixed methods integration, and program theory refinement is presented in Figure 3.

This study was approved by the Advisory Committee on Information Processing in Health Research and by the French National Commission for Data Protection. Ethical approval for all participating sites was granted by the Research Ethics Committee of Lyon University Hospital (Hospices Civils de Lyon, approval 22‐5143). The FASTRACS-RCT received separate and dedicated ethical approval under the clinical trial regulatory framework [25].

Participants will receive verbal and written information outlining the study objectives, data confidentiality, and their right to withdraw at any time. In accordance with French regulations for noninterventional research, written consent is not required for participation in qualitative interviews. Oral informed consent will be obtained at several stages of the study. First, participants’ agreement to be contacted will be obtained by the clinical research associate involved in the FASTRACS-RCT. Approximately 1 week later, the researcher conducting the interview will contact participants again to confirm their willingness to participate and arrange the interview. At the beginning of each interview, study objectives, confidentiality procedures, and the voluntary nature of participation will be reiterated, and participants will be explicitly asked whether they still agree to participate before audio-recording begins.

RECOVA-BCS participants will provide written consent before any contact is made with individuals involved in their RTW trajectory (eg, health care professionals, workplace stakeholders, or relatives). No personal information disclosed by RECOVA-BCS participants will be shared with these individuals during interviews, and all data will be anonymized and securely stored in a collaborative workspace.

Given the potentially sensitive nature of discussions related to health status, work experiences, and RTW difficulties, particular attention will be paid to participants’ emotional well-being during interviews. The coordination team includes physician-researchers with clinical experience in mental health and supportive care. In the event of emotional distress or psychological difficulties identified during data collection, participants may be referred to appropriate care pathways or health care professionals, if needed.

Any substantial protocol amendment will be submitted for renewed ethics approval, and participant information materials will be updated accordingly.