The U.S. FDA has granted 510(k) clearance to a blood-based biomarker assay for disease monitoring of patients with metastatic breast cancer (MBC). The Divitum Tka assay, developed by Uppsala, Sweden-based Biovica International AB, measures the activity of the enzyme thymidine kinase-1 (TK1) which is highly associated with cell proliferation and a predictive marker of tumor aggressiveness. It is the first liquid cancer cell proliferation biomarker assay to be approved by the FDA for use in monitoring metastatic breast cancer.