Introduction

Approximately one in three people globally lives with a chronic physical illness [1]. Chronic physical illness has been described as an assault on the body that threatens the integrity of self [2] and forces a reconstruction and reappraisal of one’s identity and health status [3]. Perceiving one’s illness as severe has been negatively associated with self-esteem, life satisfaction, and psychological wellbeing [4], with prevalence of chronic disease sharing a direct, positive effect with psychological distress [5]. Living with chronic physical illness brings with it many burdens, such as financial pressure, deterioration of quality of life, medication adherence, inability to work, and need for symptom control [1]. This leaves those who live with chronic disease at a higher risk of depression and anxiety, in comparison to those who do not [6,7]. Further, the relationship between chronic physical illness and mental health may be bidirectional. For example, depression has been shown to be associated with factors such as decreased metabolic control and monitoring, medication adherence, and increased hospitalisation over time [8].

While psychological outcomes like anxiety and depression are of great relevance to those affected by chronic physical illness (e.g., migraine, endometriosis) [9,10], they are not the only factors to affect these individuals. For instance, fear of cancer recurrence (FCR), concern about patients’ illness progressing or recurring [11], was found to be the most common psychological concern for individuals affected by cancer, in a systematic review of 130 articles [12]. FCR rates of up to 70% have been observed in cancer survivors [13], with meta-analytic evidence from 34 papers suggesting FCR to be negatively associated with quality of life and psychological wellbeing, and positively associated with anxiety, depression, rumination, and distress [14].

It has been proposed that cancer diagnosis engenders an existential crisis, triggering awareness of mortality, and invoking relevant defensive behaviours, such as avoidance and attempts to build meaning [15]. Indeed, existential concerns seem central to the experience of FCR. Existing qualitative research has examined the experience of FCR in 30 breast cancer survivors [16]. While those with low FCR levels spoke about practical concerns, such as treatment, disruptions to family life and finances, participants with moderate to high FCR expressed concern around death and the dying process [16]. They spoke fearfully about the prospect of cancer recurrence, worrying about potential death and the impact it could have on friends, family and colleagues, suggesting potential links between FCR and death-related concerns among those having recovered from cancer [16].

While research on FCR has largely focused on cancer, fear of progression or recurrence (FOPR) is a broader phenomenon affecting individuals with various chronic conditions. A meta-analysis of 12 studies found FOPR in various illnesses other than cancer, including coronary heart disease, stroke and Diabetes, to be positively associated with anxiety and negatively associated with quality of life [17]. Further insight to the experience of FOPR is granted by the paper’s narrative synthesis of qualitative data from over 9,000 participants across 25 studies, which similarly highlighted the relevance of FOPR across various disease types [17]. Echoing previous research examining FOPR in cancer survivors [16], death anxiety also appeared highly relevant to the experience of FOPR in illnesses other than cancer [17]. Participants voiced concerns about their awareness of death, and how their potential death would impact their families, as a result of illness progression or recurrence. These findings are further reinforced by a scoping review of 37 articles which found fear of death to be one of the seven most prominent fears associated with fear of illness progression in cardiac patients [18]. And so, despite the literature’s predominant focus on FOPR in relation to cancer, the existing literature, while limited, suggests death anxiety’s relevance FOPR in chronic, physical conditions other than cancer [17,18].

In sum, existing systematic reviews in this field have focused more broadly on the relationship between FOPR and mental health outcomes [17], and/or exclusively evaluated these outcomes in the context of cancer [14]. While emerging evidence suggests that death anxiety is relevant to FOPR in certain illnesses, a systematic evaluation of this relationship across chronic conditions is lacking. Further, whether death anxiety is uniquely related to terminal illnesses, such as cancer, or equivalently in other chronic physical illnesses has yet to be examined. Fears of death are particularly pertinent to explore, given that death anxiety has attracted growing recognition as a transdiagnostic construct, playing a key role in numerous psychopathologies [19]. This has led to burgeoning calls for treatments specifically targeting death anxiety, with evidence suggesting death anxiety can be effectively reduced through cognitive behaviour therapy interventions [20,21]. It is therefore essential to explore whether death anxiety is significantly associated with FOPR across physical illnesses. If a relationship is shown to exist between death anxiety and FOPR, this may help to identify potential new treatment targets, to reduce FOPR, and to improve mental health and wellbeing for those with chronic physical illnesses.

Methods and analysis

The Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) guidelines were followed when developing this protocol [22,23]. The protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO; CRD42024583393).

Types of studies

The acronym PECO (Population, Exposure, Comparisons, Outcome) guided the inclusion and exclusion criteria of this systematic review and meta-analysis protocol (Table 1). Only peer-reviewed quantitative studies, including cross-sectional, experimental, quasi-experimental and intervention studies, written in the English language, will be included. Qualitative studies, policy briefs or reports, opinion papers, commentaries, editorials, news, theoretical papers, conference presentations, dissertations, literature reviews, systematic reviews and meta-analyses will be excluded. Non-English records will also be excluded. There will be no date limit placed on this search.

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Table 1. Eligibility criteria for the systematic review and meta-analysis.

https://doi.org/10.1371/journal.pone.0325176.t001

Discussion

This study aims to systematically examine the association between death anxiety and FOPR, based on available quantitative evidence, and to calculate an effect size for this association, should sufficient data be available.

Existing qualitative research paints death anxiety as being a key part of the experience of FOPR. However, available quantitative evidence examining associations between death anxiety and FOPR has yet to be synthesised, leaving the extent of their association unclear. Strong associations between death anxiety and mental health symptomology have previously been identified [19]. Further, death anxiety has been shown to be transdiagnostic across numerous types of psychopathologies [26] and its importance in conceptualising and treating mental illness has been proposed [27]. Thus, systematically evaluating whether death anxiety is associated with FOPR will aid in understanding illness-related concerns and mental health of individuals affected by chronic physical illness, and may aid in improving their wellbeing.

A strength of this review is its intention to include all types of chronic physical illness and, if there are enough studies for inclusion, examine whether the size of the association between death anxiety and FOPR differs between illness types (e.g., life-threatening vs. non-life-threatening). Gender, age and other available demographic variables may also be tested as potential moderators of the effect.

Given the breadth of research linking both FOPR and death anxiety to negative outcomes, it is worth establishing whether a significant association exists between them. In the general population, death anxiety has been shown to be effectively reduced through cognitive behaviour therapy interventions [20]. Further, other psychological interventions, particularly those focusing on creating meaning, have been shown to significantly alleviate death anxiety in patients with advanced cancer [28,29]. Thus, if a relationship is found between death anxiety and FOPR, then targeting death anxiety may have clinical implications for improving the treatment of illness concerns and broader mental health. For example, it may pave the way for future research examining whether treating death anxiety directly leads to benefits in alleviating FOPR. In addition, should differences be found in the size of relationship between death anxiety and FOPR between cancer and other chronic physical illnesses, future research may also consider whether targeting death anxiety leads to significantly different improvements in FOPR and broader mental health as a function of disease type.

Finally, the current review will also allow for an examination of the current scope of research in this area. In doing so, it will identify certain types of illnesses that are potentially under-represented in the literature at present and pave the way for future research with benefit to further understand factors associated with FOPR and to lend itself to improving the overall wellbeing of people living with chronic physical illness.

Supporting information