A recurrence occurs when cancer comes back after treatment. This can happen weeks, months, or even years after the primary or original cancer was treated. It is impossible to know for sure if the cancer will recur and timely detection of recurrence, as well as identification of patients at high risk of recurrence after surgery, can be challenging. Postsurgical circulating tumor DNA (ctDNA) analysis is a promising tool for the identification of patients with minimal residual disease. Now researchers at Massachusetts General Hospital (MGH) report they have evaluated the first test that detects cancer DNA circulating in the blood of patients following treatment without knowing the particular mutations that were present in the patient’s tumor.