This week Nick Burr and Bjorn Rembacken are discussing the bright new world of molecular screening for occult cancers as the NHS starts screening for more than 50 cancers.  This summer the “Galleri blood test”, developed by an American company called ‘GRAIL’ will be piloted on 140.000 healthy people in the UK.   Naturally, Bjorn remains sceptical, and after an unsuccessful search for the ‘study aims’, asks if getting a positive result always mean that the cancer is treatable?  Furthermore, how do you tell the difference between a true positive and a false positive?  Surprisingly, we are also standing up for the effectiveness of CTC and wonder why an American study reports such shockingly poor results.