Background
Cancer-related fatigue (CRF) is a common and disturbing late effect in cancer patients and survivors which is often underdiagnosed and undertreated [
1,
2]. CRF is defined as “a distressing, persistent, subjective sense of physical, emotional, and/or cognitive tiredness or exhaustion related to cancer or cancer treatment that is not proportional to recent activity and interferes with functioning” according to the National Comprehensive Cancer Network (NCCN) [
3]. CRF usually diminishes in the first year after treatment completion, yet a previous study has shown that 24% of childhood cancer survivors continued to experience CRF up to two decades after cancer diagnosis [
4]. The etiology of CRF is multi-factorial and poorly understood [
1]. Biological, demographic, psychosocial, and behavioral factors influence the development of CRF among cancer patients and survivors [
1]. For this reason, there is no “gold standard” of treatment; however, several approaches, such as exercise, psychosocial interventions, and mind–body interventions, showed positive effects reducing fatigue [
1]. To accurately identify fatigued survivors, implementing regular screening for CRF in long-term follow-up care of childhood and adolescent cancer survivors (CCS) is recommended [
5].
Reported prevalence of CRF in CCS varies widely in the literature—from 0 to 62% [
6]. Variability in prevalence is due to differences in study designs, methodology, and fatigue-measuring instruments. Until 2020, there was no unified recommendation regarding which fatigue-measuring instrument to use in CCS [
5]. Therefore, a large number of instruments including the Checklist Individual Strength (CIS), or the numerical rating scale (NRS), were in use. Recent guidelines for surveillance of CRF among childhood, adolescent, and young adult cancer survivors by the International Guideline Harmonization Group (IGHG) show knowledge gaps about factors associated with CRF for this population [
5]. Many treatment-related, clinical, and sociodemographic factors have been studied as contributors of cancer-related fatigue in CCS, such as anxiety, pain, and educational level [
5,
7]. However, psychological distress is the only factor with high quality of evidence available [
5]. Other associated factors, such as late effects, pain, older age, radiotherapy, and sleep problems, have moderate or low levels of evidence [
5]. It is likely that the etiology of cancer-related fatigue is multifactorial [
1,
8,
9], and sufficient evidence on CRF prevalence and factors associated with it is crucial for establishing and updating clinical guidelines on CRF in CCS, such as those from the IGHG. Therefore, in this study, we aimed to evaluate the prevalence of CRF and factors associated with CRF among CCS.
Discussion
We found that about one-fifth of CCS reported increased CRF many years after cancer diagnosis, while none reported severe CRF. Female survivors, survivors of CNS tumors, and those with sleep disturbance or endocrine disorders had more CRF than others. Older age at study was associated with lower levels of CRF compared with those aged < 30 years.
Since study populations differ by age, cancer treatments and diagnoses, and outcome definition, reported prevalence of CRF among adult CCS varies widely [
6]. Comparing results from current studies is also difficult because up to eight different questionnaires were used in CRF prevalence studies [
6]. Similar to our study, Lopez-Guerra et al. found no participant reported severe CRF [
28], yet only included 17 long-term survivors of Ewing sarcoma with a median age at study of 19 years. Calaminus et al. found 4% of participants severely fatigued in a cohort of 725 Hodgkin lymphoma survivors with median age at study of 28 years [
29]. However, in large studies unrestricted by including survivors of only one cancer diagnosis, the prevalence of severe CRF was higher [
6]. In the North America-based Childhood Cancer Survivor Study (CCSS), 14% of 1821 adult CCS (mean age at study: 35 years) were identified as severely fatigued using the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F) instrument [
30]. In the Dutch CCS study (DCCSS-LATER), 26% of 2516 adult CCS (median time since diagnosis: 22 years) were identified as severely fatigued using the Short Fatigue Questionnaire (SFQ) [
4]. In the British CCS study (BCCSS), 33% of 9920 adult CCS (median age at study: 33 years) were identified as severely fatigued using the Short Form 36 Health-status Survey (SF-36) [
31]. Since these studies used different fatigue-measuring instruments, reported prevalences fluctuated strongly. The fluctuations emphasize the need for a harmonized assessment of CRF among CCS to better understand CRF prevalence among adult CCS.
Our study showed female sex was associated with higher CRF levels. This has been described before in CCS, but the overall level of evidence is very low according to IGHG criteria [
5,
32‐
38]. In the general population, females also more often report CRF, yet the reason is unclear [
39,
40]. It does not appear solely attributable to health conditions that have a higher prevalence in women and are known to be associated with fatigue (e.g., depression) [
41]. We further saw higher CRF levels among CNS tumor survivors when compared with survivors of leukemia. While the recently published article by van Deuren et al. reports statistically significant association between CRF and previous diagnosis of a CNS tumor in adult CCS, Mulrooney et al. report association which is not statistically significant, and Langeveld et al. report no association [
4,
35,
36].
Sleep disturbance and endocrine disorders were associated with increased CRF in our study. Meeske et al. also reported a significant association between sleep disturbance and CRF among 161 adult survivors of acute lymphoblastic leukemia (OR = 6.15; 95% CI 2.3–16.2) [
42]. Since clustering of CRF and sleep problems is well documented among adult cancer survivors, the low level of evidence for associations between sleep disorders and CRF among adult CCS that Christen et al. reported is surprising [
5,
43‐
46]. As for endocrine disorders, the literature differs on the spectrum of endocrine disorders considered. While Mulrooney et al. and Hamre et al. showed no association of hypothyroidism with CRF, Sato et al. showed an association of endocrine abnormality with CRF among CCS [
33,
35,
47]. Among endocrine disorders that we assessed in our study, diabetes mellitus and hypothyroidism had the strongest correlation with CRF in subsequent multivariable linear regression models replacing the general endocrine disorder variable with individual endocrine disorders that we performed ex post (Supplementary Tables
4A–F).
In our study, age at study was also associated with CRF severity. The literature on the topic of age at study is conflicting. When looking at the available studies, it is important to differentiate whether this variable was assessed as continuous or categorical. As for age at study as a continuous variable, Hamre et al. and Johansdottir et al. showed a weak but statistically significant positive association of older age at study with CRF (OR 1.04; 95% CI 1.0–1.1 and 1.08; 95% CI 1.01–1.16 respectively) [
34,
48]. Two studies showed no significant association of older age with CRF which is in line with the finding of our univariable model [
33,
36]. The weak association with age at study as a continuous variable might be caused by different levels of CRF expressed over the course of life. As we showed in our multivariable analysis, CRF follows a U-shaped pattern across the three age categories with lowest CRF among CCS aged 30–39 years. Paradoxically, the recent study by van Deuren et al. showed an upside-down U-shaped pattern across age categories in terms of CRF prevalence [
4]. This paradox could be caused by different study designs since van Deuren et al. assessed prevalence of CRF in a national cohort whereas our study is a single-center study of survivors at a cardio-oncology clinic. Further studies are needed to clarify the course of CRF over lifetime.
Strengths and limitations
Our study is the first study on prevalence and factors associated with CRF among Swiss adult CCS. Since the study setting allowed gathering high-quality and reliable data on treatment exposures, current medical histories, anthropometry, and CCS lifestyles, the study setting was valuable. It allowed analyzing details from a spectrum of possible factors associated with CRF when compared with studies with only self-reported data. However, the study setting was also a limitation since the main study interest was assessing cardiovascular health during outpatient clinic visits. For this reason, survivors had to accept the invitation and attend the outpatient clinic after which they received the fatigue questionnaire—a potentially significant obstacle for severely fatigued survivors and likely contributor to the relatively low participation rate of 30%. For this reason, severely fatigued CCS are possibly underrepresented in our study. However, when comparing participants with those who took part in the CardioOnco study but did not fill out fatigue-measuring instruments in the questionnaire, we can see that there are no significant differences between these two populations. The study design possibly introduces further selection bias, since CCS treated with surgery only were excluded, yet current research shows no effect of surgical treatment on CRF among CCS [
5]. CCS with shorter time since diagnosis, e.g., of 5 to 9 years, were less represented in our cohort than those with longer time since diagnosis. This may have underrepresented the presented CRF prevalence since the risk for CRF decreases with time since diagnosis [
5].
Conclusion
We showed a substantial proportion of survivors suffer from increased levels of CRF that might interfere with their daily functioning. We identified demographic and clinical factors associated with increased CRF which could help to better identify CCS at risk for CRF. Identifying CRF-associated factors is important for the development of CRF surveillance guidelines and ensuring better tailored follow-up care of CCS. In summary, healthcare professionals need to be aware of the increased risk of CRF among adult survivors of childhood cancer and should actively screen CCS, particularly female survivors, < 30 years old, CNS tumor survivors, and survivors with sleep disturbance or endocrine disorders.
Acknowledgements
We thank all survivors for participating in our study, the study team of the Childhood Cancer Research Group (Luzius Mader, Selma Riedo, and Andrea Ziörjen), the data managers of the Swiss Pediatric Oncology Group (Claudia Althaus, Nadine Assbichler, Pamela Balestra, Heike Baumeler, Nadine Beusch, Sarah Blanc, Susann Drerup, Janine Garibay, Franziska Hochreutener, Friedgard Julmy, Eléna Lemmel, Rodolfo Lo Piccolo, Heike Markiewicz, Veneranda Mattielo, Annette Reinberg, Renate Siegenthaler, Astrid Schiltknecht, Beate Schwenke, Monika Imbach, and Verena Stahel), and the team of the Swiss Childhood Cancer Registry (Meltem Altun, Erika Brantschen, Katharina Flandera, Anna Glenck, Elisabeth Kiraly, Ursula Kühnel, Eleftheria Michalopoulou, Erika Minder, Shelagh Redmond, and Cornelia Stadter). We also want to thank the author of the Checklist Individual Strength questionnaire—Jan Vercoulen—for answering our questions regarding the questionnaire. We thank Kristin Marie Bivens for her editorial work on our manuscript.
This publication is dedicated to the memory of the late Jiří Sláma, Department of Archeology, Faculty of Arts, Charles University, Czech Republic.
Publisher's note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.