Circulation check.

What’s the best endpoint for prostate cancer studies, anyway? Despite its iffy clinical significance, PSA is often used because it’s just so darn quick and easy to measure. But now there’s a new blood test in town, and last week’s JCO pub aimed to put it to the test. We are, of course, talking about liquid biopsies (aka cell-free or circulating tumor DNA). A secondary analysis of five recent prospective randomized clinical trials for patients with metastatic castration-resistant prostate cancer compared eight different binary ways of interpreting PSA and liquid biopsies at 0 and 13 weeks from trial intervention. The winning correlate of decreased overall survival: any measurable circulating tumor DNA at both 0 and 13 weeks. Despite this test’s own drawbacks, it may eventually enable us to distinguish early which patients merit more intensive therapy.