Be skeptical of those cancer blood tests

Stephan Savoia / AP

We've heard a lot about the Silicon Valley startups, like Freenome and Grail, that are raising tons of money to develop a blood test that can detect cancer. But BuzzFeed takes a closer look this morning and finds a reason to be skeptical: The companies aren't really saying how they're going to do that.

Why it matters: Cancer researchers say that kind of a test would be extremely hard to develop. That's why it would be so valuable, of course, but it's also why the research community would really like more details.