The biological basis underlying cognitive dysfunction in women with early-stage breast cancer (BC) remains unclear, but could reflect gene expression changes that arise from the acquisition and long-term retention of soma-wide alterations in DNA methylation in response to chemotherapy. In this longitudinal study, we identified differences in peripheral methylation patterns present in women prior to treatment (T1) and 1 year after receiving chemotherapy (T4) and evaluated relationships among the differential methylation (DM) ratios with changes in cognitive function. A total of 58 paired (T1 and T4) blood specimens were evaluated. Methylation values were determined for DNA isolated from whole blood using a genome-wide array . Cognitive function was measured using the validated, computerized CNS Vital Signs platform. Relationships between methylation patterns and cognitive domain scores were compared using a stepwise linear regression analysis, with demographic variables as covariates. The symptom comparison analysis was restricted to 2,199 CpG positions showing significant methylation ratio changes between T1 and T4. The positions with DM were enriched for genes involved in the modulation of cytokine concentrations. Significant DM ratios were associated with memory domain (56 CpGs). Eight of the ten largest DM ratio changes associated with lack of memory improvement were localized to genes involved in either neural function (ECE2, PPFIBP2) or signalling processes (USP6NL, RIPOR2, KLF5, UBE2V1, DGKA, RPS6KA1). These results suggest that epigenetic changes acquired and retained for at least one year in non-tumour cells following chemotherapy may be associated with a lack of memory improvement following treatment in BC survivors.
Keywords: Breast cancer; DNA methylation; chemo-brain; chemotherapy; cognitive function; epigenetics.