IMpassion130 was approved on an assay called SP142. That’s an assay which was used in the trial and it classified 40% of the population as PD-L1 positive on their immune cells. So that was the population that derived the benefit from the addition of atezolizumab. The issue with PD-L1 testing is there are lots of assays and lots of ways to call positivity. What we wanted to understand in the abstract presented by Hope Rugo was how these different assays compared. So we looked at SP263 and the 223C assay which is the Merck assay. I won’t bore you in the specifics but basically we found that SP142 classified the least number of patients as positive, 263 and the 223C assay classified about 60% more patients as positive. When you look at the benefit of atezolizumab the hazard ratios do look roughly the same across all assays which suggests to me that potentially more people can benefit. But if you look specifically at the patients that were negative by the 142, which is the approved assay, and positive by the other assays it does seem that their hazard ratios are a little bit larger. So maybe they don’t benefit as much.

The 142 assay is reading out a truly sensitive population. It’s difficult to understand how we’re going to implement that in the clinic because obviously pathologists find they have to buy different equipment. Specifically for breast it may be harder to get reproducibility so a positive over here in this lab may not be the same as another lab and that’s, of course, important for patients. It means less patients potentially would get the drug. But we need to understand a bit more whether we can find other markers that will help us understand who will benefit. So overall it was a nice study to look at the different assays but at the end of the study we feel that the assay used in IMpassion does pick out a sensitive population that will benefit from the addition of atezolizumab.