Blood test trial aims to detect cancer recurrence before it happens

At Princess Margaret Cancer Centre in Toronto, a five-year study called SHERLOCK is enrolling 7,000 cancer survivors in a search for something medicine has long struggled to offer: certainty. By drawing blood repeatedly and scanning it for microscopic traces of tumor DNA invisible to conventional imaging, researchers hope to learn whether this knowledge can guide treatment — sparing some patients from unnecessary therapies while catching recurrence in others before it takes hold. It is, at its core, a wager that better information is more merciful than the silence that follows a clean scan.