ctDNA in Breast Milk for Early Detection of Pregnancy Associated Breast Cancer

Abstract Pregnancy associated breast cancer (PABC) is an overall poor prognosis group compared to non-PABC breast cancer (BC), mainly due to late diagnosis. Effective screening approaches for early detection may improve its outcome. For the first time, we demonstrate the presence of cell-free tumor DNA (ctDNA) in the breast milk serum (sBM) of PABC in patients with early-stage disease and its ability to recapitulate somatic mutations present in the primary tumor. Moreover, our results demonstrate that sBM robustly surpasses plasma for tumor genetic profiling due to a prevalent shedding of ctDNA into the sBM in localized disease, as well as increased total cell-free DNA (cfDNA) abundance and integrity. Thus, we propose sBM as a potential new non-invasive liquid biopsy for a prompt detection of PABC.