Low tumor mitochondrial DNA content is associated with better outcome in breast cancer patients receiving anthracycline-based chemotherapy

Purpose: In this study, we aimed to explore whether low levels of mitochondrial DNA (mtDNA) content in the primary tumor could predict better outcome for breast cancer patients receiving anthracycline-based therapies. We hypothesized that tumor cells with low mtDNA content are more susceptible to mitochondrial damage induced by anthracyclines, and thus are more susceptible to anthracycline treatment. Experimental Design: We measured mtDNA content by a qPCR approach in 295 primary breast tumor specimens originating from two well-defined cohorts: 174 lymph node–positive patients who received adjuvant chemotherapy and 121 patients with advanced disease who received chemotherapy as first-line palliative treatment. The chemotherapy regimens given were either anthracycline-based (FAC/FEC) or methotrexate-based (CMF). Results: In both the adjuvant and advanced settings, we observed increased benefit for patients with low mtDNA content in their primary tumor, but only when treated with FAC/FEC. In multivariable Cox regression analysis for respectively distant metastasis-free survival and progression-free survival, the HR for the FAC/FEC-treated mtDNA low group in the adjuvant setting was 0.46 [95% confidence interval (CI), 0.24–0.89; P = 0.020] and in the advanced setting 0.49 (95% CI, 0.27–0.90; P = 0.022) compared with the FAC/FEC-treated mtDNA high group. We did not observe these associations in the patients treated with CMF. Conclusions: In our two study cohorts, breast cancer patients with low mtDNA content in their primary tumor had better outcome from anthracycline-containing chemotherapy. The frequently observed decrease in mtDNA content in primary breast tumors may be exploited by guiding chemotherapeutic regimen decision making.

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