A virus walks into a Barr.

August 15, 2017. In our primer on “liquid biopsies” a few weeks back we noted that the concept, while promising, has many challenges. A landmark success story for liquid biopsy screening for nasopharyngeal cancer (NPC) in Hong Kong was published this week in NEJM. NPC is closely associated with Epstein-Barr virus infection, particularly in Southeast Asia. In short, environmental factors make epithelial cells susceptible to persistent EBV infections, which allows the virus to integrate its genome and induce further proliferation. Eventually, tumors form and shed DNA that, on average, carries about 50 copies of the viral DNA. While detecting EBV DNA or antibodies in patients with NPC is old news, this study is pivotal in its description of a successful screening regimen that detected persistent circulating tumor DNA. With over 20,000 people screened, the positive predictive value was 11% (pretty good for large-scale screening). And 47% of screening-detected cases were Stage I, i.e. highly curable...and highly divergent from most NPC presentations (~80% advanced disease). So, at least in endemic areas, screening for circulating tumor DNA can identify NPC at an earlier stage and lead to more cures. Cheers to that.