Quantification of methylation-specific cardiomyocyte cell-free DNA as an early marker of cardiotoxicity in patients with breast cancer receiving anthracyclines and trastuzumab.

12090 Background: There is currently no way to reliably predict which patients undergoing therapy for breast cancer will develop cardiotoxicity. An early biomarker of cardiotoxicity could provide opportunity for intervention prior to the appearance of gross abnormalities on echocardiogram (ECHO). A droplet digital PCR (ddPCR) assay for circulating cell-free DNA (cfDNA) can detect cfDNA released from dying cardiomyocytes with high sensitivity by differentiating cfDNA of cardiomyocyte origin based on the pattern of methylation specific to the cell type. Circulating cfDNA of cardiac origin was tested as an early biomarker of toxicity in patients who underwent breast cancer treatment while closely monitoring cardiac function in a prospective clinical trial. Methods: A cardiomyocyte methylation-specific quantitative ddPCR assay was tested in plasma samples from 29 patients who were part of a larger prospectively enrolled cohort of women who received anthracyclines and trastuzumab for HER2-positive breast cancer. Blood samples were tested from prior to doxorubicin and cyclophosphamide (AC) chemotherapy, two months later after completing AC and prior to trastuzumab, and every 3 months to 12 months post-treatment. Patients were assessed for clinical cardiotoxicity, defined as heart failure (NYHA class III/IV) or significant EF decline (> = 10% to below 53% or > = 16%) until completion of cancer therapy. The maximum detected level of cardiac cfDNA (copies per 500 µL plasma) was compared between those who experienced cardiotoxicity and those who did not by two-sided T-tests. Results are reported as mean +/- standard deviation. Results: At baseline, cardiac cfDNA levels were low (mean 1.1 +/- 2.4 copies). Of 29 patients, five developed clinical cardiotoxicity. The maximum number of cfDNA copies at any time point was elevated in patients who experienced cardiotoxicity compared to those who did not (mean of 20.6 +/- 7.3 copies versus 9.3 +/- 9.8 copies, p = 0.0216). Of the patients with cardiotoxicity, elevated cfDNA of greater than 10 copies was detected an average of 3.6 +/- 2.5 months prior to the onset of clinical cardiotoxicity. Conclusions: Methylation specific cardiac cfDNA shows promise as an early indicator of cardiotoxicity in patients treated with anthracyclines in this pilot study. A previously reported analysis in the levels of seven other biomarkers including high-sensitivity troponin I and NT-proBNP pre- versus post-treatment in the full cohort of 80 patients did not show any statistically significant associations with the development of cardiotoxicity, suggesting that cardiac cfDNA may be uniquely informative. Clinical trial information: NCT02177175.