Grail, a Menlo Park, Calif.-based developer of blood tests to detect cancer at its earliest stages, has raised $900 million in Series B funding. ARCH Venture Partners and includes Johnson & Johnson Innovation co-led the round, which could grow even larger with Goldman Sachs serving as placement agent. Other backers include Bristol-Myers Squibb, Merck, Celgene, Tencent, Amazon, McKesson and Varian Medical Systems.

Why it's a big deal: Liquid biopsies are so hot right now. Just yesterday we noted that Freenome had raised $65 million for its own efforts. The potential breakthrough is screening otherwise-healthy people for cancer, which should significantly improve treatment efficacy. The complications include reimbursement and the medical argument that unncessary biopsies (i.e., for those healthy folks who don't have cancer in their furure) are needlessly dangerous.

Bottom line: "Grail needs the huge war chest to fund an exceedingly difficult quest. It is conducting large, long trials to test the worth of a blood test meant to catch cancer when it's most treatable—long before patients show any symptoms—by detecting fragments of cancer DNA shed by tumors." — Ben Fidler