Association of mitochondrial DNA content in peripheral blood with cancer-related fatigue and chemotherapy-related cognitive impairment in early-stage breast cancer patients: a prospective cohort study.

PURPOSE: Cancer-related fatigue (CRF) and chemotherapy-related cognitive impairment (CRCI) are reported to be associated with mitochondrial dysfunction. Hence, mitochondrial DNA (mtDNA) content, a biomarker of mitochondrial dysfunction, is hypothesized to correlate with the onset of CRF and CRCI. This study aims to evaluate the association between peripheral blood mtDNA content reduction and severity of CRF and CRCI in patients receiving chemotherapy. METHODS: This was a prospective cohort study. Early-stage breast cancer patients receiving anthracycline- or taxane-based chemotherapy were recruited. CRF was assessed using MFSI-SF, and CRCI was assessed using FACT-Cog and CANTAB at two timepoints: baseline (T1; prior to treatment) and 6 weeks after initiation of treatment (T2). mtDNA content was measured at both timepoints using real-time quantitative polymerase chain reaction. Multiple logistic regression was utilized to evaluate the association between mtDNA reduction and worsening of CRF and CRCI, adjusting for age, anxiety, insomnia, plasma cytokines concentrations, and other clinically important covariates. RESULTS: A total of 108 patients (age 52.0 ± 9.2 years; 82.4% Chinese; 64.8% receiving anthracycline-based chemotherapy) were recruited. Proportions of patients with worsening of CRF increased from the lower to the upper quartiles of mtDNA reduction (22.2, 33.3, 55.6, and 63.0% in quartiles 1, 2, 3, and 4, respectively, p = 0.001 for trend). Reduction of mtDNA content was significantly greater among those with worsening of CRF and CRCI compared to those without CRF [mean reduction (± SD): 36.5 (46.1) vs. 9.4 (34.5), p < 0.001]. After adjusting for covariates, every 1-unit reduction of the mtDNA content was associated with a 4% increased risk for worsening of CRF (95% CI, 1-6%; p = 0.009). CONCLUSIONS: This is the first study to show that the reduction of mtDNA content in peripheral blood is associated with the onset of CRF in patients receiving chemotherapy. Further validation studies are required to confirm the findings.