The first aim of the current study was to determine whether we could identify subgroups of patients on the basis of their pattern of fatigue following treatment for breast cancer. The results indicated that two groups of patients could be identified. One group reported relatively low levels of fatigue immediately after completing treatment. Over the next 6 months, these low levels declined slightly. By contrast, the other group reported much higher levels of fatigue immediately after treatment. Although they too demonstrated a decline in fatigue during the follow-up period, this improvement did not persist between 4 and 6 months, and at 6 months this group continued to report relatively high levels of fatigue.
The identification of two groups of patients with distinct patterns of fatigue is consistent with the findings of Helgeson, Snyder, and Seltman (2004)
. In this study, the authors assessed women’s psychological and physical adjustment to breast cancer over 4 years. Although the majority of the women showed fairly consistent improvement in mental and physical functioning over time, the researchers identified subgroups of women who showed distinct patterns of change. For example, with respect to changes in physical functioning, one group demonstrated better physical functioning at baseline (4 months postdiagnosis), improved slightly over time, and remained high until the end of the follow-up period. Another group demonstrated a lower level of physical functioning at baseline and did not change over time. Helgeson et al. (2004)
also found that personal and social resources, but not demographic or disease variables, distinguished the different trajectories or patterns of mental and physical functioning.
The second aim of the study was to examine whether the subgroups identified could be distinguished on the basis of demographic, clinical, and psychosocial factors. In univariate analysis, the extent of catastrophizing at treatment completion predicted different trajectories of fatigue (i.e., group membership) across the 6-month follow-up period. As hypothesized, higher fatigue catastrophizing scores at the end of treatment predicted membership in the high-fatigue group. Physical exercise was a statistically significant predictor (p < .045) of fatigue group membership in the univariate analysis, providing support for the hypothesis that less physical activity at the end of treatment would be associated with more fatigue in the posttreatment period. Higher body mass index at treatment completion also emerged as a significant univariate predictor of membership in the high-fatigue group. Marital status and annual income also distinguished different trajectories of fatigue in univariate analysis. Women who were not married and had lower incomes were more likely to be in the high-fatigue group. In the multivariate analysis, only fatigue catastrophizing and body mass index remained as statistically significant predictors of fatigue group membership across the 6-month follow-up period.
In addition to identifying groups of women who differ significantly in their experience of fatigue following treatment for breast cancer, findings regarding the role of certain factors in perpetuating fatigue in the posttreatment period partially validate the proposed cognitive–behavioral model. Previous research has suggested that catastrophizing about fatigue may be a risk factor for greater fatigue after treatment (Broeckel et al., 1998
; Jacobsen et al., 2004
; Jacobsen et al., 1999
). However, with the exception of one study (Jacobsen et al., 2004
), the existing research has been cross-sectional in design. The results of the current study indicate that catastrophizing about fatigue during the active treatment period has implications for the experience of fatigue following treatment completion. There is a growing body of research documenting that physical activity has a positive effect on fatigue in individuals with cancer. Researchers have found that individuals who report less physical activity during or after treatment report greater levels of fatigue (Berger, 1998
; Berger & Higginbotham, 2000
; Dimeo et al., 1997
; Schwartz, 1998
). Likewise, there is growing evidence that interventions designed to increase activity levels have had beneficial effects on fatigue in cancer patients (for a review, see Irwin & Ainsworth, 2004
). In this study, however, increased physical activity at the time of treatment completion was a significant predictor of lower levels of fatigue in the subsequent 6-month period in the univariate analysis but did not remain a significant predictor in the multivariate analysis.
As noted previously, several other factors besides catastrophizing were significant predictors of fatigue group membership in univariate analysis. The relationship of marital status and income with fatigue observed in the present study is consistent with the findings of Bower et al. (2000)
and de Jong, Candel, Schouten, Huijer Abu-Saad, and Courtens (2004)
. In general, however, previous research has not found a relationship between fatigue and demographic variables (for a review, see Servaes, C. Verhagen, & Bleijenberg, 2002
). In the current study, it may be the case that women who are married and have higher incomes have greater access to interpersonal and material resources that may assist them in ultimately reducing their fatigue. Previous studies investigating differences in fatigue among breast cancer survivors on the basis of treatment modality have yielded mixed results (Andrykowski et al., 1998
; Berglund, Bolund, Fornander, Rutqvist, & Sjoden, 1991
; Bower et al., 2000
; Woo, Dibble, & Piper, 1998
). In the current study, women who received both chemotherapy and radiotherapy were indistinguishable in terms of their fatigue class membership from women who received radiotherapy only. It may be the case that differences emerge only later than 6 months posttreatment. Consistent with previous research (e.g., Broeckel et al., 1998
; Mast, 1998
; Okuyama et al., 2000
), we did not find a relationship between the use of hormone therapy and fatigue group membership. Although weight gain is a common problem among women treated with chemotherapy for early stage breast cancer (Kumar et al., 2004
; Lankester, Phillips, & Lawton, 2002
; McInnes & Knobf, 2001
), we did not hypothesize that body mass index would be associated with fatigue following treatment. The few studies that have investigated this relationship have yielded mixed results (Andrykowski et al., 1998
; Kumar et al., 2004
; Wratten et al., 2004
). The results of the current study, particularly the finding that body mass index was the only demographic and clinical variable to remain a significant predictor in the multivariate analysis, lend further support for the view that greater body mass index is significantly associated with worse fatigue following treatment.
The current study has important clinical implications. According to the National Comprehensive Cancer Network Clinical Practice Guidelines for Cancer-Related Fatigue (National Comprehensive Cancer Network, 2003
), persons who rate their fatigue as 4 or higher on a 10-point scale deserve further evaluation, in terms of a focused history and physical examination. At 6 months following treatment, 44% of women in the high-fatigue group provided scores of 4 or greater on the item that assessed average fatigue in the past week, and 59% of women in the high-fatigue group provided scores of 4 or greater on the item that assessed most fatigue in the past week. By contrast, no members of the low-fatigue group rated their fatigue as 4 or higher on either item. Thus, the results indicate that not only are these groups statistically distinct, but a sizable proportion of the high-fatigue group merits further evaluation for their fatigue. To better appreciate the relative differences in fatigue, we also compared the fatigue reported by the high-fatigue group with self-reported fatigue scores from a sample of women (n
= 85; mean age = 57.4 years) with no history of cancer matched for age and geographic residence with participants from the current study. On the composite measure of the four fatigue items, this healthy noncancer group averaged 2.42 (SD
= 1.62), compared with 3.19 (SD
= 2.19) for the high-fatigue group at the 6-month posttreatment follow-up. Similarly, whereas the healthy noncancer group reported an average fatigue score in the past week of 2.53 (SD
= 1.94), the high-fatigue group reported an average level of fatigue of 3.23 (SD
A considerable body of research has documented a relationship between catastrophizing and the experience of pain (Sullivan & D’Eon, 1990
; Sullivan et al., 2001
) and demonstrated that interventions based on cognitive–behavioral models can lead to reductions in catastrophizing that are associated with better adjustment to chronic pain (Jensen, Turner, & Romano, 2001
). Research in chronic pain also suggests that certain behaviors such as activity reduction are related to catastrophizing and may serve to exacerbate pain. Taken together, these findings suggest that similar interventions designed to reduce reliance on catastrophizing and reduce weight may be effective in reducing fatigue in women completing treatment for early stage breast cancer. Accordingly, promoting increases in physical activity as a means of facilitating weight loss should be viewed as a potential intervention strategy. The current study also demonstrates the usefulness of growth mixture modeling for the longitudinal study of quality of life outcomes in cancer patients. As noted previously, similar methods have been used successfully to identify groups of breast cancer survivors who differ in their psychological and physical adjustment over time and to identify predictors of group membership (Helgeson et al., 2004
). The pattern of results seen in the present study highlights that there are considerable individual differences in the way people experience fatigue following treatment for breast cancer. Statistical analytic techniques that permit examination and prediction of patterns of response over time, such as growth mixture modeling, are likely to prove useful for examining changes in other aspects of quality of life, such as sexual functioning and cognitive functioning.
Certain limitations of the current study should be noted. The women in our sample predominately were Caucasian, were married, and had annual household incomes over $40,000. Whether our findings are generalizable to a more diverse population of women with early stage breast cancer survivors is not known. A strength of the current study is its longitudinal design and the repeated assessments during the posttreatment period. However, we assessed fatigue only until 6 months after treatment. Whether different patterns of fatigue emerge later in the course of cancer survivorship is unclear.
In conclusion, the present study identified two groups of breast cancer patients on the basis of their patterns of fatigue. One group experienced relatively low levels of fatigue at the end of treatment and throughout the follow-up period, whereas the other group experienced relatively high levels of fatigue at the end of treatment that persisted throughout the 6-month follow-up period. Consistent with a cognitive–behavioral model, patients in the high-fatigue group were more likely to rely on fatigue catastrophizing. These findings suggest that efforts should be aimed at the development and evaluation of interventions to reduce patients’ reliance on catastrophizing as a cognitive coping strategy. Similarly, interventions to minimize treatment-related increases in body mass index, perhaps via increases in physical activity in the active treatment period, may prove useful in reducing fatigue in the posttreatment period.