This study examined the relationship between symptoms of FoP and GAD among cancer patients by applying network analysis. The graphical presentation of the network can be interpreted in the way that the FoP symptoms form a distinct syndrome that can be discriminated from GAD, an assumption supported in previous relevant work [15], [17]–[19], [23].
However, the comparability of our results with previous studies is limited. Most importantly, except for one[23] all of these studies investigated the relationship between the two constructs based on categorial diagnoses or assessment measures’ sum scores [15], [17]–[19].
Yang and colleagues were so far the first research group who investigated the interrelations between FoP, GAD and depression [23]. In line with our results, they found only a few and weak associations connecting FoP with GAD and depression, which the authors interpreted as FoP being a distinct syndrome. Since FoP was assessed in only a four-item scale in sample of female breast cancer patients the applicability to our results is limited, but provides support for our hypothesis.
A finding that can be found in all mentioned works is a statistical relevant proportion of cancer patients suffering from clinical levels of FoP that cannot be explained by an underlying or comorbid anxiety disorder such as GAD[15], [17]–[19]. These findings underpin the assumption of FoP as a distinct syndrome as it neither cannot be understood as a subsyndromal form of GAD nor be captured within the boundaries of established anxiety disorders. In summary, all previous findings on that topic rely on the concept of group comparisons (only FoP vs. only mental disorder vs. both) [15], [17]–[19]. Since there is no commonly agreed clinical definitions of elevated FoP, groups were created by using varying thresholds on respective sum scores. Regardless of the relevance of these works, the findings cannot be used to draw conclusions about potential interaction between symptoms and no specific hypotheses on underlying mechanisms that FoP might share with GAD. This makes a discussion of hypotheses that could be used to discriminate both syndromes challenging. Thewes and colleagues discuss that cancer patients who experience clinical levels of FoP do not engage in pathological worry that refers to events, situations or problems of daily life as GAD does and thus argue that worries of cancer patients are focused particularly on cancer recurrence [17]. In addition, the research group among Simard examined the phenomenology of intrusive thoughts associated with FoP in a large sample of heterogeneous cancer patients (N = 1984; breast, prostate, lung and colorectal) by using cluster analysis [35]. They found that intrusive thoughts associated with FoP were very similar to worries, which could partially explain the assumed closeness to GAD.
Following the suggestion of Thewes and colleagues we hypothesized that FoP and GAD could be discriminated based on worry content, i.e., cancer-related vs. non-cancer related. In line with our a priori assumption, the rather unspecific GAD symptom worry about many things was among the symptoms that were least associated with FoP symptoms.
With respect to the cancer-related worries, our hypotheses were also largely confirmed: That is, all pre-selected symptoms (e.g., disease progression or medical follow-ups) had the smallest associations with GAD symptoms. However, these findings were only partly validated by our conservative statistical approach. In combination with the spatial organization of the symptom networks, however, our overall findings may be interpreted as an indicator for FoP being a distinct syndrome from GAD.
Besides our pre-selected cancer-specific symptoms, we also found that worries related to Pain and Dying were only weakly associated with GAD symptoms. A potential explanation might be that the former two symptoms may be also highly relevant among cancer patients even though the disease is not explicitly mentioned in the questions. This assumption is in line with a work that found fear of pain and death to be the most frequently reported fears among cancer patients [36].
With respect to indicators of co-occurence between both syndromes, we identified the symptoms Fear of awful events and Irritability. The FoP symptom Irritability shares a strong association with the GAD symptom Annoyance.
The GAD symptom Fear of awful events was strongly associated with the FoP symptoms Attack by anxiety, Irritability and Hypervigilance, which provides support for potential co-occurrence pathways between both syndromes, i.e., strongly associated items may be able to activate one another in a (causal) way.
Although our cross-sectional data does not allow assumptions about the direction of the relationships, some assumptions may be made according to hypothesis established in previous research: For example, in a cross-sectional study with lymphoma patients (N = 108), anxiety symptoms at baseline predicted clinically relevant FoP within the first three years of survivorship [37]. This is in line with a mentioned study which found that anxious cancer patients often show catastrophizing cognitive pattern, where negative outcomes seem inevitable According to the Authors, it is conceivable that fear of awful events leads to increased self-attention, intrusive anxiety and irritability[36]. A possible alternative explanation for Fear of awful events as a bridging symptom would be that it is a pathway that can lead to generalization of anxiety, so that a GAD develops from the experience of FoP.
Our findings support the conception of FoP as a distinct syndrome, which subsequently makes it relevant for further elaboration of psychotherapeutic concepts that might address FoP directly [16]. Regarding differential diagnostics in cancer patients, it seems helpful to explore the content of worries in more detail. The clinical relevance of the present work lies primarily in the fact that symptoms have been identified that potentially play a central role in both constructs. It has been stipulated that the targeted treatment of symptoms with a strong linkage in the network may lead to a secondary reduction of associated symptoms [38]. To the best of our knowledge, our study was the first that examined symptoms of FoP and GAD in hematological cancer survivors with the statistical approach of network analyses. We defined a priori hypotheses based on current research in order to be as theory-driven as possible despite the explorative character of our study. The hypotheses were tested both descriptively, but also statistically validated using a very conservative approach. Another particular strength of the present work is our large sample of patients which enabled sufficient test power for this type of analyses. Additionally, stability analyses allowed to select those indices for presentation that were considered stable and thus interpretable.
4.1. Limitations
As a major limitation, the cross-sectional data does not allow any conclusions about causal relationships between symptoms. Characteristics that predispose people to develop FoP or GAD cannot be displayed. Moreover, our sample is highly specific, as it includes exclusively hematological cancer survivors and is therefore not representative for other cancer sites. Nevertheless, our data could establish valuable hypotheses that can be validated in future longitudinal studies. The factor-analytic approach to questionnaire construction may also had an influence on the symptom clustering in our symptom network, as symptom clusters in networks can be indicators of underlying latent variables [22]. Even though the GAD-7 and FoP-Q are psychometrically validated, these complex constructs are captured by relatively few symptoms and thus many potentially relevant details on their respective characteristics are lost. For future studies, it might be fruitful to use extended questionnaires with more detailed items to explore the dynamics between FoP and GAD in a more profound way. For example, metacognitions seem to play an important role in theoretical models of the development and maintenance of both constructs and should be therefore considered when selecting instruments to be used in future relevant symptom networks [7], [39].
4.2. Conclusion
In this study applying network analysis, we could largely confirm previous research assuming that FoP is a distinct syndrome in cancer patients that may be differentiated from GAD. Therefore, it seems reasonable to systematically screen cancer patients not only for GAD but also for FoP. Furthermore, we identified symptoms that may play a central role in the network. Future longitudinal studies are needed to verify our hypotheses driven but exploratory findings.