Background
With nearly three quarters of a million people diagnosed in 2008, colorectal cancer is estimated to be the most common incident cancer in the developed world [
1]. In 2008 there were an estimated 3.3 million people living with a diagnosis of colorectal cancer within the previous 5 years [
1]. Although there has been a decrease in incidence rates in Australia [
2], as in the United States [
3], the numbers of people diagnosed with colorectal cancer (CRC) each year continue to increase [
2]. Despite having one of the highest incidence rates in the world [
1], survival outcomes for Australians diagnosed with colorectal cancer are relatively high compared to other countries [
4]. Survival expectations increase the longer they survive, so that CRC cancer patients who have survived seven years after diagnosis can anticipate similar 5-year survival outcomes to the general population [
5]. The high prevalence of this disease brings into sharp focus the issue of how colorectal cancer influences long term quality of life.
A recent systematic review of quality of life (QOL) outcomes for long term colorectal cancer survivors concluded that long term QOL overall is good for these patients, but noted that research to date was limited by being largely cross sectional in design [
6]. Predictors of poorer outcomes included: younger age, lower income and a smaller social network. A longitudinal study of CRC patients over a ten year period found that CRC survivors reported stable or improved QOL over the first three years from diagnosis, however from three to ten years function declined [
7]. Younger age at diagnosis (<60 years) was found to be predictive of poorer QOL across role, social, emotional, and cognitive functioning and on this basis it was concluded that longitudinal development of QOL was dependent upon age at diagnosis. Our team identified that baseline QOL was a strong predictor of QOL five years after treatment, with gender, private health insurance, social support, and threat appraisal influencing various QOL domains [
8]. However, by comparison to the previous study [
7] no effect was found for age. Hence, there is still lack of clarity about who is most at risk for poorer long term outcomes.
In this regard, optimism presents as a dispositional trait that influences both psychological and quality of life outcomes after cancer [
9‐
11]. Optimism is defined as the generalized expectancy that more good things than bad will happen in the future [
12]. The effect of optimism on outcomes appears to be mediated by threat appraisal [
13], such that more optimistic people form more positive appraisals about the consequences of their cancer, and the likely outcomes, and from this experience less distress compared to people who are more pessimistic. Finally, social support is also an important and well accepted antecedent of both psychological and HR-QOL outcomes [
9], such that the social environment in which a person lives may help (if positive) or hinder (if negative) the adjustment process.
In assessing QOL after cancer, two measurement approaches present: health-related quality of life and life satisfaction. Health-related quality of life (HR-QOL) is a multi-dimensional construct that incorporates, at minimum. the social, psychological and physical aspects of health [
14]. On this view, these different aspects of HR-QOL make up layers of well-being that influence a person’s health status and that when disrupted by disease are expressed as decrements in these domains of quality of life. Accordingly, measurement approaches for HR-QOL tend to be domain and symptom-based, matching these layers. Over the past three decades a wealth of research, on a global scale, has emerged seeking to accurately measure HR-QOL, some of which has developed more generic approaches relevant to a person with any illness status [
15], and some if which is tied to a specific disease, such as cancer and the various cancer types [
16].
By contrast, life satisfaction is conceptualized as the outcome of a person’s judgment about the extent to which their current life quality matches their self-imposed life standards [
17]. Hence, by contrast to the quite specific measurement approach used in HRQOL, assessment of life satisfaction is more global and relates more to internal individual standards that are likely, at least in part, dispositional. As an example, one person may perceive that if they were unable to function physically in a certain way that their life would be intolerable, whereas another person might view these functions as less crucial. The actual physical changes may be the same, however the judgment of what these changes mean differs, and hence so does the person’s overall life satisfaction.
Our study assessed the five year trajectories of both HR-QOL
and life satisfaction in long term colorectal cancer survivors’ adjustment using an analytic approach known as growth mixture modelling [
18]. Socio-demographic variables as well as optimism, threat appraisal and social support were included as predictor variables. In this approach we aimed to provide a more complete understanding of the QOL implications of colorectal cancer, both health-related and subjective, over time and more clearly identify what subgroups of patients are at risk for poorer outcomes.
Discussion
Three quarters of all CRC survivors experienced consistently medium to high HR-QOL for the five years after their cancer diagnosis; and one in five had consistently poorer outcomes with a smaller group declining in HR-QOL at three years. Hence, it appears that while many CRC survivors do well over time, a sizeable subgroup carry a substantive long term health burden. Characteristics that placed individuals at risk of these negative outcomes were clear: poorer psychological resources predicted a more negative long term trajectory of QOL for CRC survivors. This was the case for the person’s subjective judgment of their QOL, as well as their HR-QOL; and suggests that in order to improve these outcomes, interventions early in the illness experience to improve these resources are needed. In this context, interventions based on social cognitive theory may be most salient [
31]. Therapy targets here include self-efficacy [
32], outcome expectations [
33], and self-regulation [
32], with meta-analyses suggesting strategies that target these components are associated with better outcomes [
31]. Support interventions that promote optimism and hope in a supportive group or dyadic peer setting may also be indicated, where peer interaction acts as the mechanism for change through the processes of social comparison and social support [
34].
Younger age was confirmed also as a risk factor for poorer QOL outcomes, a finding that is consistent with other cancer types and likely related to life stage demands and expectations [
35,
36]. Specifically, younger CRC survivors may still be building careers and families, have greater financial responsibilities, and also see their cancer as occurring out of age-related usual expectations for health and illness events. A novel finding was that remoteness of residence and socioeconomic disadvantage uniquely predicted poorer outcomes for the colorectal specific quality of life domain that reflects disease-specific iatrogenic effects. This seems consistent with findings that increasing remoteness of residence and area-based social disadvantage are independently associated with lower colorectal cancer survival [
37]. The reasons for this are unclear, however, evidence that patients living outside major cities have a higher risk of advanced colorectal cancer at diagnosis[
38] and also that survival decreases with increasing distance to the patient’s closest radiotherapy treatment facility [
39] suggest that differential access to diagnostic and treatment services are possible factors. Hence, these patients may experience greater disease burden as a result of poorer access to optimal medical treatment.
While the patterns for prediction for life satisfaction were similar to that for HR-QOL, there were some substantive differences. First, almost half of all participants reported constant high life satisfaction. Specifically, for these individuals the experience of having cancer did not lead them to judge their lives globally as being impaired or less than ideal, based on their own values or internal standards. For those participants whose life satisfaction trajectories varied over time (both declining and increasing) they seemed to return largely to their baseline state at five years. This suggests two conclusions. First, that while life satisfaction may respond to external events changes (such as a cancer diagnosis), it is a temporally stable phenomenon [
40]. This finding adds to the body of knowledge about our understanding of life satisfaction as a construct. Second, this may also speak to individuals’ resilience to cancer. Resilience is broadly conceptualized as the ability to sustain trauma without developing reactive psychopathology [
41]. Previous research comparing cancer survivors to an age, gender and education matched sample, concluded that while survivors do experience impaired psychological functioning in some domains, such as social wellbeing, they are resilient [
42]. The ability of cancer survivors to maintain a stable sense of life satisfaction after their cancer experience may also, at least in part, reflect resilience.
In this regard, a limitation of the present study is that we did not specifically measure resilience such that our picture of what factors matters most in predicting quality of life outcomes may be incomplete. This is an area for future research. As well, although we were able to recruit a substantive study sample it is possible that those who did not participate varied in important ways, for example may have been more distressed or less health literate. As we did not have data on non-respondents we were unable to assess this. However, key strengths of this study include the prospective design with long term follow up, application of well validated and reliable measures, and a large population based sample.
In conclusion, the present results add to the growing body of knowledge about the heterogeneous nature of individual adjustment after cancer and further highlight the importance of considering inter-individual differences in research with this population group, as well as in planning service delivery. The contrast between trajectory patterns for HR-QOL and life satisfaction suggests that they are distinct adjustment outcomes. Life satisfaction appears in this population group to be temporally stable and this may reflect individuals’ psychological resilience to the experience of cancer. There is growing recognition of the importance of patient-focused outcomes in cancer care [
43]; where the quality of a person’s life and the personal preferences and values of that person guide their health care. The inclusion of life satisfaction in future research as a distinct adjustment outcome based on the individual’s point of reference is warranted.
Competing interests
Authors’ disclosures of potential conflicts of interest: The author(s) indicated no potential conflicts of interest.
Authors’ contributions
JD conceived the project, participated in its design and coordination and led manuscript development; SKN performed the statistical analysis and guided interpretation of results; PB JA and PY participated in its design and coordination, provided methodological guidance and helped to draft the manuscript: WB provided direction towards analyses and intellectual comment for interpretation of results; SKC directed the study, its design and coordination, and helped to draft the manuscript. All authors read and approved the final manuscript.