Over the 26 month period following breast cancer diagnosis, our data show that depressive symptomatology as measured by the BDI, is generally low and stable for women over age 65, and decreases slightly for women aged 55–64. While initially high for women aged 24–54, BDI scores greatly decrease, but still remain higher, on average, than for older women up to 26 months after diagnosis. The decrease observed among younger women occurs mostly in the first year following diagnosis with minimal decline thereafter.
In our subsequent modeling, we sought to understand whether these age differences remained after controlling for a wide range of covariates and to identify factors that might explain these age differences. Adjustment for covariates that were associated with age at diagnosis and that were themselves significant independent predictors of depressive symptoms rendered the age × time effect statistically nonsignificant. Consistent with our previous baseline manuscript [8
], trouble paying for basics, chemotherapy with doxorubicin, and greater symptom levels, lower sense of meaning and peace, greater illness intrusiveness, and greater use of passive coping at baseline were related to depressive symptoms.
The addition of our time varying variables showed that completion of chemotherapy with doxorubicin and declines in pain and vasomotor symptoms were associated with decreased depressive symptoms. Completion of chemotherapy without doxorubicin was not associated with change in depressive symptoms, highlighting the more significant side effects of doxorubicin.
Changes in the psychosocial variables were also related to changes in depressive symptoms. Increases in sense of meaning and peace and in social support were associated with decreased depressive symptoms. Yanez et al. [28
] also found that women who showed an increased sense of meaning and peace had decreased depression over 6 months following treatment for breast cancer. Although others have shown in longitudinal studies that social support from family and friends is associated with better emotional health [7
], this study provides evidence that increased
social support over time is also related to decreased depressive symptoms. Consistent with Low [29
], we also found that passive coping was associated with depressive symptoms, but adding to the literature, we also found that within-individual increases in passive coping were related to increased depressive symptoms. Within-person decline in illness intrusiveness also predicted significant decline in depressive symptoms. These results suggest specific areas of intervention focus that could potentially lead to reduced depression.
This study has several limitations. The Beck Depression Inventory is a self-report measure of depressive symptomatology and is not a measure of clinical depression. Although characteristic of many samples of breast cancer patients, this sample is relatively homogeneous (mostly white and educated) which limits the generalizability of our findings. Another limitation is that women were only followed up to approximately 26 months post diagnosis. Although the greatest decline in depressive symptoms is shown to occur within the first year after diagnosis and these data cover the time period that women transition from active treatment to survivorship, additional follow-up would provide data on a longer-time trajectory. Finally, these are data from an observational study and it is not possible to draw definitive conclusions regarding direction of causality for some associations (e.g., pain and depression). For such associations, causality may even be bi-directional.
Women completed the first survey up to 8 months post diagnosis, meaning there was no constant baseline with respect to date of diagnosis. However, by using months since diagnosis rather than survey as our marker of time, we were able to analyze the data using an appropriate common time metric.
Strengths of this study include the large sample size and repeated measures of depressive symptoms and a wide range of predictors collected longitudinally over a 26 month period following diagnosis. This length of follow-up enabled us to capture time following end of treatment. Despite finding that age was not independently related to change in depression over time in our adjusted analyses, this result does not mean age is unimportant. In the “real world,” younger women are indeed more likely to present with depression following breast cancer diagnosis than older women, because they are more likely to present with factors (illness intrusiveness, chemotherapy with doxorubicin, pain) that are highly significant independent predictors of depression. Our full model, where age differences over time are rendered (statistically) non-significant, sheds light on why the commonly-found age-depression relation exists. Such understanding may suggest potential avenues for intervention/focus for all women who present, after a breast cancer diagnosis, with factors highly predictive of depression. Young women will be more likely to fall into such a category.