Identification of Somatic Mutations in Thirty-year-old Serum Cell-free DNA From Patients With Breast Cancer: A Feasibility Study

INTRODUCTION: The aim of this study was to assess the feasibility of cell-free DNA (cfDNA) extraction and circulating tumor DNA sequencing in 30-year-old serum samples. MATERIALS AND METHODS: We evaluated serum samples from 52 patients with breast cancer, which were collected between 1983 and 1991, with correlating clinicopathologic data. cfDNA was extracted by using the QIAamp Circulating Nucleic Acid Extraction Kit (Qiagen). Of these 52 cfDNA samples, 10 were randomly selected and sequenced with the Oncomine Breast cfDNA Assay (A31183). In a second step, high-depth targeted sequencing of 15 additional cfDNA samples was performed using a custom Ampliseq Ion Torrent panel targeting breast cancer-related genes. RESULTS: cfDNA extraction was successful in 52 (100%) of 52 patients with a total concentration of 0.2 to 54 ng/uL. A total of 24 cancer-specific mutations were found in 22 (88%) of the 25 samples undergoing sequencing. Of the 52 patients, 32 (62%) had died from breast cancer after a median follow-up of 7.9 years (interquartile range, 3.7-15.5 years). CONCLUSION: The present study shows that current next generation sequencing technology is sufficiently robust and specific to analyze 30-year-old serum. Therefore, longitudinal studies can be designed with storage of serum samples over many years, thereby obviating the need for timely and continuous cfDNA extraction and sequencing. The samples can be pooled and processed at once with the most modern technology available at the end of the study, when accumulation of events allows correlation of clinical outcomes with adequate power.