Consistent with other research, in this sample cognitive abilities remained within normal limits for a majority of breast cancer survivors in the year following treatment. A modest percentage of participants did evidence lower than expected performance in neuropsychological functioning, although a majority of these individuals were evidencing subtle deficits (defined as z
= −1.00 to −1.49, per Vardy and colleagues [40
]). There was some indication of improvements in neuropsychological test scores over the year following treatment, as RCI analyses of individuals’ data revealed that a small portion of individuals demonstrated statistically reliable improvements. This is commensurate with findings from other research and highlights the importance of looking at individual test scores rather than group means [16
]. However, these findings are considered preliminary. While the RCI analyses help account for measurement error, the absence of a control group in this research precluded the use of RCI analyses that would take into account practice effects for this sample. It is possible that the improvements in test scores reflect the effects of repeated exposure to tests rather than clinical significant gains in cognitive functioning.
As previously noted, the intent of this project was to bring attention to the question of whether subtle neuropsychological difficulties evidenced by breast cancer survivors were clinically/functionally significant. To this end, analyses were conducted to determine whether neuropsychological test performance was associated with concurrent self-reported emotional functioning, social role functioning, and quality of life. In addition, recognizing that cognitive difficulties do not occur in isolation, the potential contributions of fatigue, self-reported cognitive complaints, and social support seeking were also considered important in evaluating quality of life outcomes. The resulting regression models revealed that, consistent with other research [30
], social support was significantly related with several aspects of quality of life and social role functioning at 6 months and 12 months post-chemotherapy. Also consistent with other work [27
] were findings that fatigue continued to negatively affect physical well-being and functional well-being among breast cancer survivors 6 and 12 months post-chemotherapy.
Of greatest relevance in terms of the aims of the present research were findings suggesting that self-reported cognitive complaints and neuropsychological test performance may be associated with some aspects of quality of life in the year following chemotherapy. Self-reported cognitive complaints have been associated with emotional distress in other studies [9
], but this is one of the few studies that documents its potential relationship to a related construct, quality of life. Specifically, these data indicated that self-reported cognitive difficulties were associated with poorer emotional well-being among this sample of breast cancer survivors at 12 months post-chemotherapy.
In addition, although only a small portion of study participants evidenced cognitive abilities that were below expectations over the year following chemotherapy, regression analyses indicated that ongoing difficulties with verbal fluency may be associated with poorer functional well-being 12 months post-chemotherapy. In considering these findings, it is important to recognize that < 20% of study participants’ test scores were considered below expectations (i.e., z < −1.00) on any given test at each time point, suggesting that the frequency of cognitive difficulties was low. However, from a treatment perspective, it could be argued that this finding may be noteworthy nonetheless. Specifically, if these findings are replicated in future studies, it would suggest that providers may have an opportunity to improve survivors’ outcomes by monitoring cognitive functioning over time and considering treatment if indicated.
Despite some potentially thought-provoking findings, the present study has several limitations that deserve mention. In terms of the study sample, although consistent with the methodology of approximately one-half of published studies in this area that were recently reviewed [16
], the absence of a control group limits the extent to which these findings can be identified as specific to the population of women cancer survivors status post chemotherapy. In other words, factors unrelated to cancer and/or its treatments may be contributing to subjective cognitive complaints as well as documented neuropsychological test performance difficulties. On the other hand, from a purely pragmatic perspective, if cognitive difficulties are leading to poorer quality of life in cancer survivors, it could be argued that they warrant attention regardless of the etiology.
In addition, findings from the regression analyses would be considered more conclusive if the relationships between neuropsychological tests scores and/or subjective cognitive complaints were significantly associated with a greater percentage of our outcome measures. This highlights the preliminary nature of these findings and the need for follow-up research to determine whether these relationships are replicated with other samples. However, it is also worth noting that our ability to detect cognitive decline and its relationship to functional outcomes may have been hampered by the nature of our sample. First, because this particular sample was relatively well educated, it is possible that their baseline cognitive abilities were higher than average, which could obscure evidence of cognitive decline (i.e., modest cognitive decline could result in performances that remained within normal limits). This issue may be minimized in future studies by including a pre-treatment baseline assessment of cognitive abilities. In addition, analyses indicated that individuals who dropped out after 1 month were evidencing significantly poorer verbal fluency (see footnote), suggesting that we may not have retained individuals who were experiencing greater difficulties after treatment.
The relatively small size of the sample, particularly by the 12 month time point, is another limitation of the study. Substantial efforts were made to retain participants, but this was a difficult task given the nature of patients served in the cancer centers in our community (many come from rural populations far from the facilities where they are treated). Future studies can endeavor to minimize the impact of this issue by reducing burden on participants (e.g., by offering to travel to their homes for data collection). Related to this, a relatively high number of variables were included in the analyses given the small sample size. Efforts were made to lessen the risk of a Type II error by creating composite test scores for the neuropsychological domains and minimizing the number of other predictor variables included in each equation. Additionally, all variables were selected based on a priori hypotheses derived from an understanding of prior research in this area.
An additional statistical concern that occurs with longitudinal studies involving neuropsychological testing lies in our ability to account for practice effects on tests. Efforts were made to minimize the risk of practice effects by utilizing alternate forms where possible (e.g., Rey AVLT, COWAT, Category fluency), but practice effects likely played a role in some of the improvements documented, particularly in WAIS-III scores. Future studies can address concerns regarding practice effects by: (1) minimizing their occurrence through the use of alternate forms, and (2) including a control group that would allow for RCI analyses that can statistically account for these effects.
Given these limitations, findings from this study are considered preliminary. However, when considered in the context of other research documenting women's concerns that cognitive difficulties following treatment are affecting their quality of life [26
], they highlight the need for further exploration of possible relationships between cognitive difficulties following cancer treatment and functional outcomes. In addition, future research may focus on understanding factors that contribute to the experience of neuropsychological test deficits and self-reported cognitive complaints among cancer survivors. This important work of identifying risk factors can lead to interventions offered before and/or during the course of treatment that could potentially lessen the impact of cancer and/or its treatment on cognitive functioning, thereby improving quality of life outcomes for cancer survivors.