Plasma levels of interleukin-6 mediate neurocognitive performance in older breast cancer survivors: The Thinking and Living With Cancer study

Abstract

Background: Immune activation/inflammation markers (immune markers) were tested to explain differences in neurocognition among older breast cancer survivors versus noncancer controls.

Methods: Women >60 years old with primary breast cancer (stages 0-III) (n = 400) were assessed before systemic therapy with frequency-matched controls (n = 329) and followed annually to 60 months; blood was collected during annual assessments from 2016 to 2020. Neurocognition was measured by tests of attention, processing speed, and executive function (APE). Plasma levels of interleukin-6 (IL-6), IL-8, IL-10, tumor necrosis factor α (TNF-α), and interferon γ were determined using multiplex testing. Mixed linear models were used to compare results of immune marker levels by survivor/control group by time and by controlling for age, racial/ethnic group, cognitive reserve, and study site. Covariate-adjusted multilevel mediation analyses tested whether survivor/control group effects on cognition were explained by immune markers; secondary analyses examined the impact of additional covariates (e.g., comorbidity and obesity) on mediation effects.

Results: Participants were aged 60-90 years (mean, 67.7 years). Most survivors had stage I (60.9%) estrogen receptor-positive tumors (87.6%). Survivors had significantly higher IL-6 levels than controls before systemic therapy and at 12, 24, and 60 months (p ≤ .001-.014) but there were no differences for other markers. Survivors had lower adjusted APE scores than controls (p < .05). Levels of IL-6, IL-10, and TNF-α were related to APE, with IL-6 explaining part of the relationship between survivor/control group and APE (p = .01). The magnitude of this mediation effect decreased but remained significant (p = .047) after the consideration of additional covariates.

Conclusions: Older breast cancer survivors had worse long-term neurocognitive performance than controls, and this relationship was explained in part by elevated IL-6.

Keywords: breast cancer; cancer-related cognitive decline; cognition; immune activation; inflammation; older survivors.

Figure 1. CONSORT Diagram of Older Breast Cancer Survivors and Non-Cancer Controls from the TLC Study included in Analyses of the Relationships between Immune Markers and Cognition.

The final analytic sample had biomarker results for one or more blood draws. Reasons for not having blood drawn among those consenting to blood collection included not being able to obtain the specimen, and participant not having time or wanting to skip the blood draw. Since blood specimens were not obtained until 2016 under a protocol revision, participants enrolled from 2010 to 2015 may have already completed the study, decided not to continue or have died or dropped out prior to blood collection. Panel A. Survivors Panel B. Non-cancer Controls

Figure 2.. Adjusted Natural Log-transformed Immune Marker Levels by Timepoint for Older Breast Cancer Survivors vs. Older Non-Cancer Controls

Results of linear mixed effects model analyses in survivors (red, n=399 total due to one missing WRAT4 score) and non-cancer controls (blue, n=328 or 329 total due to missing values for IL-10 or TNF-alpha) at each study visit (baseline, 12-, 24-, 36-, 48- and 60-months), including an interaction of survivor/control group by time and adjusted for age, race (White vs. non-White), cognitive reserve (WRAT4 Word Reading score), and study site. Mean adjusted immune marker levels at each timepoint are plotted on the natural log scale (ln pg/mL) as indicated on the left y-axis, and error bars show the standard error (SE). For ease of interpretation, equivalent non-transformed pg/mL values are shown on the right y-axis. P values from the mixed models for survivor vs. control differences in adjusted immune marker levels at each study visit are shown along the x-axis. Please see Supplemental Figure 2 for box plots, and Supplemental Table 1 for sample sizes at each timepoint. Panel A. IL-6 Panel B. IL-8 Panel C. IL-10 Panel D. TNF-alpha Panel E. Interferon (IFN)-gamma

Figure 2.. Adjusted Natural Log-transformed Immune Marker Levels by Timepoint for Older Breast Cancer Survivors vs. Older Non-Cancer Controls

Results of linear mixed effects model analyses in survivors (red, n=399 total due to one missing WRAT4 score) and non-cancer controls (blue, n=328 or 329 total due to missing values for IL-10 or TNF-alpha) at each study visit (baseline, 12-, 24-, 36-, 48- and 60-months), including an interaction of survivor/control group by time and adjusted for age, race (White vs. non-White), cognitive reserve (WRAT4 Word Reading score), and study site. Mean adjusted immune marker levels at each timepoint are plotted on the natural log scale (ln pg/mL) as indicated on the left y-axis, and error bars show the standard error (SE). For ease of interpretation, equivalent non-transformed pg/mL values are shown on the right y-axis. P values from the mixed models for survivor vs. control differences in adjusted immune marker levels at each study visit are shown along the x-axis. Please see Supplemental Figure 2 for box plots, and Supplemental Table 1 for sample sizes at each timepoint. Panel A. IL-6 Panel B. IL-8 Panel C. IL-10 Panel D. TNF-alpha Panel E. Interferon (IFN)-gamma

Figure 2.. Adjusted Natural Log-transformed Immune Marker Levels by Timepoint for Older Breast Cancer Survivors vs. Older Non-Cancer Controls

Results of linear mixed effects model analyses in survivors (red, n=399 total due to one missing WRAT4 score) and non-cancer controls (blue, n=328 or 329 total due to missing values for IL-10 or TNF-alpha) at each study visit (baseline, 12-, 24-, 36-, 48- and 60-months), including an interaction of survivor/control group by time and adjusted for age, race (White vs. non-White), cognitive reserve (WRAT4 Word Reading score), and study site. Mean adjusted immune marker levels at each timepoint are plotted on the natural log scale (ln pg/mL) as indicated on the left y-axis, and error bars show the standard error (SE). For ease of interpretation, equivalent non-transformed pg/mL values are shown on the right y-axis. P values from the mixed models for survivor vs. control differences in adjusted immune marker levels at each study visit are shown along the x-axis. Please see Supplemental Figure 2 for box plots, and Supplemental Table 1 for sample sizes at each timepoint. Panel A. IL-6 Panel B. IL-8 Panel C. IL-10 Panel D. TNF-alpha Panel E. Interferon (IFN)-gamma

Figure 2.. Adjusted Natural Log-transformed Immune Marker Levels by Timepoint for Older Breast Cancer Survivors vs. Older Non-Cancer Controls

Results of linear mixed effects model analyses in survivors (red, n=399 total due to one missing WRAT4 score) and non-cancer controls (blue, n=328 or 329 total due to missing values for IL-10 or TNF-alpha) at each study visit (baseline, 12-, 24-, 36-, 48- and 60-months), including an interaction of survivor/control group by time and adjusted for age, race (White vs. non-White), cognitive reserve (WRAT4 Word Reading score), and study site. Mean adjusted immune marker levels at each timepoint are plotted on the natural log scale (ln pg/mL) as indicated on the left y-axis, and error bars show the standard error (SE). For ease of interpretation, equivalent non-transformed pg/mL values are shown on the right y-axis. P values from the mixed models for survivor vs. control differences in adjusted immune marker levels at each study visit are shown along the x-axis. Please see Supplemental Figure 2 for box plots, and Supplemental Table 1 for sample sizes at each timepoint. Panel A. IL-6 Panel B. IL-8 Panel C. IL-10 Panel D. TNF-alpha Panel E. Interferon (IFN)-gamma

Figure 2.. Adjusted Natural Log-transformed Immune Marker Levels by Timepoint for Older Breast Cancer Survivors vs. Older Non-Cancer Controls

Results of linear mixed effects model analyses in survivors (red, n=399 total due to one missing WRAT4 score) and non-cancer controls (blue, n=328 or 329 total due to missing values for IL-10 or TNF-alpha) at each study visit (baseline, 12-, 24-, 36-, 48- and 60-months), including an interaction of survivor/control group by time and adjusted for age, race (White vs. non-White), cognitive reserve (WRAT4 Word Reading score), and study site. Mean adjusted immune marker levels at each timepoint are plotted on the natural log scale (ln pg/mL) as indicated on the left y-axis, and error bars show the standard error (SE). For ease of interpretation, equivalent non-transformed pg/mL values are shown on the right y-axis. P values from the mixed models for survivor vs. control differences in adjusted immune marker levels at each study visit are shown along the x-axis. Please see Supplemental Figure 2 for box plots, and Supplemental Table 1 for sample sizes at each timepoint. Panel A. IL-6 Panel B. IL-8 Panel C. IL-10 Panel D. TNF-alpha Panel E. Interferon (IFN)-gamma

Figure 3.. Schematic Representation of Models Testing Whether Survivor/Control Group Differences in Cognitive Outcomes are Mediated by the Effects of Group on Immune Markers

The figure illustrates the 2–1-1 multi-level mediation models that evaluate between group differences (Level 2) on time-varying changes in immune markers (Level 1) and cognitive outcomes (Level 1). These models test the total effect of survivor vs. control group on cognition scores (line βc), which combine independent effects of the immune marker effects (line βc’) and the product of the indirect effects of survivor/control group on the immune marker (line βa) and the effects of the marker on cognitive outcomes (line βb). The remaining effects of group on cognition after considering indirect effects of the pathway through inflammation are noted as βc’_. Significant indirect effects (βab, a product of paths a and b) and indicates that the direct relationship between survivor vs. control group and cognition scores is due in part to the effects of cancer and its treatment on immune activation and/or inflammation. Finally, the subscripts denote differences between persons (i) and those that vary across time (j).