Cancer is a heterogeneous genetic disease, and excisional biopsies provide only a snapshot in time of some of the rapid, dynamic genetic changes occurring in tumours. In addition, excisional biopsies are invasive, can’t be used repeatedly, and are ineffective in understanding the dynamics of tumour progression and metastasis. However, liquid biopsy, or blood sample tests, under development by Epic Sciences can generate actionable information for oncologists by analysing circulating tumour cells (CTCs) and fragments of tumor-cell DNA that are continuously shed by tumors into the bloodstream.